diff --git a/backend/benefit/requirements.in b/backend/benefit/requirements.in
index ba59d0e106..58c424a831 100644
--- a/backend/benefit/requirements.in
+++ b/backend/benefit/requirements.in
@@ -25,7 +25,7 @@ pdfkit
 pillow
 psycopg2
 python-dateutil
-python-stdnum
+python-stdnum>=1.19
 pyyaml
 requests
 sentry-sdk
diff --git a/backend/kesaseteli/applications/tests/test_youth_applications_api.py b/backend/kesaseteli/applications/tests/test_youth_applications_api.py
index 995c4e691c..b381f8b699 100644
--- a/backend/kesaseteli/applications/tests/test_youth_applications_api.py
+++ b/backend/kesaseteli/applications/tests/test_youth_applications_api.py
@@ -1156,6 +1156,16 @@ def test_youth_applications_reactivate_unexpired_inactive__vtj_disabled(
         "121212A899H",
         "111111-111C",
         "111111A111C",
+        "111111B111C",
+        "111111C111C",
+        "111111D111C",
+        "111111E111C",
+        "111111F111C",
+        "111111U111C",
+        "111111V111C",
+        "111111W111C",
+        "111111X111C",
+        "111111Y111C",
         # Django Rest Framework's serializers.CharField trims leading and trailing
         # whitespace by default, so we allow them here.
         "     111111-111C",
@@ -1853,6 +1863,13 @@ def test_youth_application_post_empty_required_field(
         # Not uppercase
         "111111-111c",
         "111111a111C",
+        # Invalid century character
+        "111111/111C",
+        "111111G111C",
+        "111111M111C",
+        "111111R111C",
+        "111111T111C",
+        "111111Z111C",
         # Invalid checksum
         "111111-111X",  # "111111-111C" would be valid
         "111111A111W",  # "111111A111C" would be valid
diff --git a/backend/kesaseteli/common/tests/test_utils.py b/backend/kesaseteli/common/tests/test_utils.py
index e89ce506bc..ec442714fe 100644
--- a/backend/kesaseteli/common/tests/test_utils.py
+++ b/backend/kesaseteli/common/tests/test_utils.py
@@ -159,7 +159,7 @@ def test_utc_datetime(args):
     assert result.tzinfo == timezone.utc
 
 
-@pytest.mark.parametrize("year", [1800, 2022, 2023, 2099])
+@pytest.mark.parametrize("year", [1800, 1987, 2022, 2023, 2024, 2025, 2099])
 def test_get_random_social_security_number_for_year(year):
     for _ in range(1000):
         result = get_random_social_security_number_for_year(year)
diff --git a/backend/kesaseteli/common/tests/utils.py b/backend/kesaseteli/common/tests/utils.py
index 66520cf37d..2617cac6a4 100644
--- a/backend/kesaseteli/common/tests/utils.py
+++ b/backend/kesaseteli/common/tests/utils.py
@@ -21,6 +21,7 @@ def get_random_social_security_number_for_year(year: int) -> str:
             tzinfo=timezone.utc,
         )
         .date(),
+        century_variant=get_faker().pyint(0, 99),  # Inclusive range
         individual_number=get_faker().pyint(2, 899),  # Inclusive range
     )
 
diff --git a/backend/kesaseteli/requirements.in b/backend/kesaseteli/requirements.in
index c1847146aa..6816dbc62e 100644
--- a/backend/kesaseteli/requirements.in
+++ b/backend/kesaseteli/requirements.in
@@ -18,7 +18,7 @@ jsonpath-ng
 mozilla-django-oidc
 pillow
 psycopg2
-python-stdnum
+python-stdnum>=1.19
 requests
 sentry-sdk
 xlsx-streaming
diff --git a/backend/kesaseteli/requirements.txt b/backend/kesaseteli/requirements.txt
index 3a8a220e82..6c8c8c068f 100644
--- a/backend/kesaseteli/requirements.txt
+++ b/backend/kesaseteli/requirements.txt
@@ -152,7 +152,7 @@ python-dateutil==2.8.1
     #   azure-storage-common
     #   faker
     #   pysaml2
-python-stdnum==1.17
+python-stdnum==1.19
     # via
     #   -r requirements.in
     #   django-localflavor
diff --git a/backend/shared/shared/common/tests/test_utils.py b/backend/shared/shared/common/tests/test_utils.py
index 34ca2606f6..9d8e3e90f0 100644
--- a/backend/shared/shared/common/tests/test_utils.py
+++ b/backend/shared/shared/common/tests/test_utils.py
@@ -97,28 +97,88 @@ def test_valid_social_security_number_birthdate(test_value, expected_result):
 
 
 @pytest.mark.parametrize(
-    "expected_result,birthdate,individual_number",
+    "expected_result,birthdate,century_variant,individual_number",
     [
-        ("010100+002H", date(year=1800, month=1, day=1), 2),
-        ("010203-1230", date(year=1903, month=2, day=1), 123),
-        ("121212A899H", date(year=2012, month=12, day=12), 899),
-        ("111111-002V", date(year=1911, month=11, day=11), 2),
-        ("111111-111C", date(year=1911, month=11, day=11), 111),
-        ("111111A111C", date(year=2011, month=11, day=11), 111),
-        ("111111-900U", date(year=1911, month=11, day=11), 900),
-        ("111111-9991", date(year=1911, month=11, day=11), 999),
-        ("300522A0024", date(year=2022, month=5, day=30), 2),
-        ("311299A999E", date(year=2099, month=12, day=31), 999),
+        ("010100+002H", date(year=1800, month=1, day=1), 0, 2),
+        ("010100+002H", date(year=1800, month=1, day=1), 99, 2),
+        ("010203-1230", date(year=1903, month=2, day=1), 0, 123),
+        ("121212A899H", date(year=2012, month=12, day=12), 0, 899),
+        ("121212A899H", date(year=2012, month=12, day=12), 30, 899),
+        ("121212B899H", date(year=2012, month=12, day=12), 1, 899),
+        ("121212B899H", date(year=2012, month=12, day=12), 31, 899),
+        ("121212C899H", date(year=2012, month=12, day=12), 2, 899),
+        ("121212C899H", date(year=2012, month=12, day=12), 32, 899),
+        ("121212D899H", date(year=2012, month=12, day=12), 3, 899),
+        ("121212D899H", date(year=2012, month=12, day=12), 33, 899),
+        ("121212E899H", date(year=2012, month=12, day=12), 4, 899),
+        ("121212E899H", date(year=2012, month=12, day=12), 34, 899),
+        ("121212F899H", date(year=2012, month=12, day=12), 5, 899),
+        ("121212F899H", date(year=2012, month=12, day=12), 35, 899),
+        ("111111-002V", date(year=1911, month=11, day=11), 0, 2),
+        ("111111-111C", date(year=1911, month=11, day=11), 0, 111),
+        ("111111Y111C", date(year=1911, month=11, day=11), 1, 111),
+        ("111111Y111C", date(year=1911, month=11, day=11), 61, 111),
+        ("111111X111C", date(year=1911, month=11, day=11), 2, 111),
+        ("111111X111C", date(year=1911, month=11, day=11), 62, 111),
+        ("111111W111C", date(year=1911, month=11, day=11), 3, 111),
+        ("111111W111C", date(year=1911, month=11, day=11), 63, 111),
+        ("111111V111C", date(year=1911, month=11, day=11), 4, 111),
+        ("111111V111C", date(year=1911, month=11, day=11), 64, 111),
+        ("111111U111C", date(year=1911, month=11, day=11), 5, 111),
+        ("111111U111C", date(year=1911, month=11, day=11), 65, 111),
+        ("111111A111C", date(year=2011, month=11, day=11), 0, 111),
+        ("111111-900U", date(year=1911, month=11, day=11), 0, 900),
+        ("111111-9991", date(year=1911, month=11, day=11), 0, 999),
+        ("300522A0024", date(year=2022, month=5, day=30), 0, 2),
+        ("300522B0024", date(year=2022, month=5, day=30), 1, 2),
+        ("311299A999E", date(year=2099, month=12, day=31), 0, 999),
+        ("311299F999E", date(year=2099, month=12, day=31), 5, 999),
+        # Go through all the possible checksum characters & before first & beyond last
+        ("111111B098Y", date(year=2011, month=11, day=11), 1, 98),
+        ("111111B0990", date(year=2011, month=11, day=11), 1, 99),
+        ("111111B1001", date(year=2011, month=11, day=11), 1, 100),
+        ("111111B1012", date(year=2011, month=11, day=11), 1, 101),
+        ("111111B1023", date(year=2011, month=11, day=11), 1, 102),
+        ("111111B1034", date(year=2011, month=11, day=11), 1, 103),
+        ("111111B1045", date(year=2011, month=11, day=11), 1, 104),
+        ("111111B1056", date(year=2011, month=11, day=11), 1, 105),
+        ("111111B1067", date(year=2011, month=11, day=11), 1, 106),
+        ("111111B1078", date(year=2011, month=11, day=11), 1, 107),
+        ("111111B1089", date(year=2011, month=11, day=11), 1, 108),
+        ("111111B109A", date(year=2011, month=11, day=11), 1, 109),
+        ("111111B110B", date(year=2011, month=11, day=11), 1, 110),
+        ("111111B111C", date(year=2011, month=11, day=11), 1, 111),
+        ("111111B112D", date(year=2011, month=11, day=11), 1, 112),
+        ("111111B113E", date(year=2011, month=11, day=11), 1, 113),
+        ("111111B114F", date(year=2011, month=11, day=11), 1, 114),
+        ("111111B115H", date(year=2011, month=11, day=11), 1, 115),
+        ("111111B116J", date(year=2011, month=11, day=11), 1, 116),
+        ("111111B117K", date(year=2011, month=11, day=11), 1, 117),
+        ("111111B118L", date(year=2011, month=11, day=11), 1, 118),
+        ("111111B119M", date(year=2011, month=11, day=11), 1, 119),
+        ("111111B120N", date(year=2011, month=11, day=11), 1, 120),
+        ("111111B121P", date(year=2011, month=11, day=11), 1, 121),
+        ("111111B122R", date(year=2011, month=11, day=11), 1, 122),
+        ("111111B123S", date(year=2011, month=11, day=11), 1, 123),
+        ("111111B124T", date(year=2011, month=11, day=11), 1, 124),
+        ("111111B125U", date(year=2011, month=11, day=11), 1, 125),
+        ("111111B126V", date(year=2011, month=11, day=11), 1, 126),
+        ("111111B127W", date(year=2011, month=11, day=11), 1, 127),
+        ("111111B128X", date(year=2011, month=11, day=11), 1, 128),
+        ("111111B129Y", date(year=2011, month=11, day=11), 1, 129),
+        ("111111B1300", date(year=2011, month=11, day=11), 1, 130),
     ],
 )
 def test_valid_create_finnish_social_security_number(
-    expected_result: str, birthdate: date, individual_number: int
+    expected_result: str, birthdate: date, century_variant: int, individual_number: int
 ):
     assert validate_finnish_social_security_number(
         expected_result, allow_temporary=True
     )
     assert (
-        create_finnish_social_security_number(birthdate, individual_number)
+        create_finnish_social_security_number(
+            birthdate, century_variant, individual_number
+        )
         == expected_result
     )
 
@@ -138,31 +198,37 @@ def test_valid_consecutive_create_finnish_social_security_number(birthdate: date
     Testing consecutive social security numbers for validity to ensure all their parts
     are calculated correctly, including the checksum (i.e. the last character).
     """
-    for individual_number in range(2, 900):
-        result = create_finnish_social_security_number(birthdate, individual_number)
-        assert len(result) == 11
-        assert validate_finnish_social_security_number(result, allow_temporary=True)
-        individual_number_from_result: int = int(result[-4:-1])
-        assert individual_number_from_result == individual_number
-        assert social_security_number_birthdate(result) == birthdate
+    for century_variant in range(0, 6):
+        for individual_number in range(2, 900):
+            result = create_finnish_social_security_number(
+                birthdate, century_variant, individual_number
+            )
+            assert len(result) == 11
+            assert validate_finnish_social_security_number(result, allow_temporary=True)
+            individual_number_from_result: int = int(result[-4:-1])
+            assert individual_number_from_result == individual_number
+            assert social_security_number_birthdate(result) == birthdate
 
 
 @pytest.mark.parametrize(
-    "birthdate,individual_number",
+    "birthdate,century_variant,individual_number",
     [
-        (date(year=1799, month=12, day=31), 2),  # Birth year < 1800
-        (date(year=2100, month=1, day=1), 2),  # Birth year > 2099
-        (date(year=2000, month=1, day=1), -1),  # Individual number < 2
-        (date(year=2000, month=1, day=1), 0),  # Individual number < 2
-        (date(year=2000, month=1, day=1), 1),  # Individual number < 2
-        (date(year=2000, month=1, day=1), 1000),  # Individual number > 999
+        (date(year=1799, month=12, day=31), 0, 2),  # Birth year < 1800
+        (date(year=2100, month=1, day=1), 0, 2),  # Birth year > 2099
+        (date(year=2000, month=1, day=1), -1, 0),  # Century variant < 0
+        (date(year=2000, month=1, day=1), 0, -1),  # Individual number < 2
+        (date(year=2000, month=1, day=1), 0, 0),  # Individual number < 2
+        (date(year=2000, month=1, day=1), 0, 1),  # Individual number < 2
+        (date(year=2000, month=1, day=1), 0, 1000),  # Individual number > 999
     ],
 )
 def test_invalid_create_finnish_social_security_number(
-    birthdate: date, individual_number: int
+    birthdate: date, century_variant: int, individual_number: int
 ):
     with pytest.raises(ValueError):
-        assert create_finnish_social_security_number(birthdate, individual_number)
+        assert create_finnish_social_security_number(
+            birthdate, century_variant, individual_number
+        )
 
 
 @pytest.mark.django_db
@@ -175,6 +241,12 @@ def test_invalid_create_finnish_social_security_number(
         "111111 -111x",  # Invalid checksum, inner whitespace
         "320522A002T",  # Invalid date because no 32 days in any month
         "311322A002E",  # Invalid date because no 13 months in any year
+        "111111/111C",  # Invalid century character
+        "111111G111C",  # Invalid century character
+        "111111M111C",  # Invalid century character
+        "111111R111C",  # Invalid century character
+        "111111T111C",  # Invalid century character
+        "111111Z111C",  # Invalid century character
         # Invalid checksum
         "111111-111X",  # "111111-111C" would be valid
         "111111A111W",  # "111111A111C" would be valid
diff --git a/backend/shared/shared/common/tests/utils.py b/backend/shared/shared/common/tests/utils.py
index 0d85aad849..ec2f9d7aa0 100644
--- a/backend/shared/shared/common/tests/utils.py
+++ b/backend/shared/shared/common/tests/utils.py
@@ -5,31 +5,54 @@
 
 
 def create_finnish_social_security_number(
-    birthdate: date, individual_number: int
+    birthdate: date, century_variant: int, individual_number: int
 ) -> str:
     """
-    Create a Finnish social security number based on birthdate and individual number
+    Create a Finnish social security number based on birthdate, century variant and
+    individual number
 
     :param birthdate: Date of birth
+    :param century_variant: Non-negative integer value for deciding which century
+                            character variant to use, e.g. birthdates in 2000–2099 may
+                            have century character A, B, C, D, E or F. There's no upper
+                            limit as (century_variant % available_century_characters) is
+                            the value being used.
     :param individual_number: Integer value where 2 <= individual_number <= 999
     :return: Finnish social security number in format <ddmmyyciiis> where
              dd = day of birth with leading zeroes,
              mm = month of birth with leading zeroes,
              yy = year of birth modulo 100 with leading zeroes,
-             c = century of birth ("+" = 1800, "-" = 1900, "A" = 2000),
+             c = century of birth, where c is
+                 "+" = 1800,
+                 "-" = 1900 if (century_variant % 6) == 0,
+                 "Y" = 1900 if (century_variant % 6) == 1,
+                 "X" = 1900 if (century_variant % 6) == 2,
+                 "W" = 1900 if (century_variant % 6) == 3,
+                 "V" = 1900 if (century_variant % 6) == 4,
+                 "U" = 1900 if (century_variant % 6) == 5,
+                 "A" = 2000 if (century_variant % 6) == 0,
+                 "B" = 2000 if (century_variant % 6) == 1,
+                 "C" = 2000 if (century_variant % 6) == 2,
+                 "D" = 2000 if (century_variant % 6) == 3,
+                 "E" = 2000 if (century_variant % 6) == 4,
+                 "F" = 2000 if (century_variant % 6) == 5,
              iii = individual number in range 2–999 with leading zeroes,
              s = checksum value calculated from <ddmmyyiii>.
     :raises ValueError: if not (1800 <= birthdate.year <= 2099)
+    :raises ValueError: if century_variant < 0
     :raises ValueError: if not (2 <= individual_number <= 999)
     """
     if not (1800 <= birthdate.year <= 2099):
         raise ValueError("Invalid birthdate year, only years 1800–2099 are supported")
+    if century_variant < 0:
+        raise ValueError("Invalid century variant, must be non-negative")
     if not (2 <= individual_number <= 999):
         raise ValueError("Invalid individual number, must be in range 2–999")
     ddmmyy: str = f"{birthdate.day:02}{birthdate.month:02}{birthdate.year % 100:02}"
     iii: str = f"{individual_number:003}"
     ddmmyyiii: str = f"{ddmmyy}{iii}"
-    century_char: str = {18: "+", 19: "-", 20: "A"}[birthdate.year // 100]
+    century_chars: str = {18: "+", 19: "-YXWVU", 20: "ABCDEF"}[birthdate.year // 100]
+    century_char: str = century_chars[century_variant % len(century_chars)]
     checksum_char: str = "0123456789ABCDEFHJKLMNPRSTUVWXY"[int(ddmmyyiii) % 31]
     return f"{ddmmyy}{century_char}{iii}{checksum_char}"
 
diff --git a/backend/shared/shared/common/utils.py b/backend/shared/shared/common/utils.py
index 7b6188c105..ed1f5217e7 100644
--- a/backend/shared/shared/common/utils.py
+++ b/backend/shared/shared/common/utils.py
@@ -15,6 +15,24 @@
 
 _ALWAYS_FALSE_Q_FILTER = Q(pk=None)  # A hack but works as primary keys can't be null
 
+# Mapping from Finnish social security number century character to century number.
+# Should be the same as stdnum.fi.hetu._century_codes but that dictionary is private.
+_CENTURY_CHAR_TO_CENTURY_NUMBER = {
+    "+": 1800,
+    "-": 1900,
+    "A": 2000,
+    "B": 2000,
+    "C": 2000,
+    "D": 2000,
+    "E": 2000,
+    "F": 2000,
+    "U": 1900,
+    "V": 1900,
+    "W": 1900,
+    "X": 1900,
+    "Y": 1900,
+}
+
 
 def any_of_q_filter(**kwargs):
     """
@@ -123,5 +141,5 @@ def social_security_number_birthdate(social_security_number) -> date:
     month = int(compacted_social_security_number[2:4])
     year_mod_100 = int(compacted_social_security_number[4:6])
     century_char = compacted_social_security_number[6]
-    century = {"+": 1800, "-": 1900, "A": 2000}[century_char]
+    century = _CENTURY_CHAR_TO_CENTURY_NUMBER[century_char]
     return date(year=century + year_mod_100, month=month, day=day)
diff --git a/backend/tet/requirements.in b/backend/tet/requirements.in
index 8377e887d9..eaad5d2dd1 100644
--- a/backend/tet/requirements.in
+++ b/backend/tet/requirements.in
@@ -16,7 +16,7 @@ filetype
 mozilla-django-oidc
 pillow
 psycopg2
-python-stdnum
+python-stdnum>=1.19
 requests
 sentry-sdk
 xlsxwriter
diff --git a/backend/tet/requirements.txt b/backend/tet/requirements.txt
index 727b013e49..19b3f69386 100644
--- a/backend/tet/requirements.txt
+++ b/backend/tet/requirements.txt
@@ -138,7 +138,7 @@ python-dateutil==2.8.1
     #   pysaml2
 python-jose==3.3.0
     # via django-helusers
-python-stdnum==1.17
+python-stdnum==1.19
     # via -r requirements.in
 pytz==2021.1
     # via
diff --git a/frontend/benefit/applicant/package.json b/frontend/benefit/applicant/package.json
index 37646d8567..18e58975a6 100644
--- a/frontend/benefit/applicant/package.json
+++ b/frontend/benefit/applicant/package.json
@@ -25,7 +25,7 @@
     "camelcase-keys": "^7.0.2",
     "date-fns": "^2.24.0",
     "dotenv": "^16.0.0",
-    "finnish-ssn": "^2.1.1",
+    "finnish-ssn": "^2.1.2",
     "formik": "^2.2.9",
     "hds-design-tokens": "^2.17.0",
     "hds-react": "^2.17.0",
diff --git a/frontend/benefit/handler/package.json b/frontend/benefit/handler/package.json
index e9ce2a1fe3..69ce5e4f08 100644
--- a/frontend/benefit/handler/package.json
+++ b/frontend/benefit/handler/package.json
@@ -23,7 +23,7 @@
     "date-fns": "^2.24.0",
     "dotenv": "^16.0.0",
     "finnish-business-ids": "^3.1.1",
-    "finnish-ssn": "^2.1.1",
+    "finnish-ssn": "^2.1.2",
     "formik": "^2.2.9",
     "fuse.js": "^6.6.2",
     "hds-design-tokens": "^2.17.0",
diff --git a/frontend/kesaseteli/handler/package.json b/frontend/kesaseteli/handler/package.json
index 70c16f97ac..82b042cb73 100644
--- a/frontend/kesaseteli/handler/package.json
+++ b/frontend/kesaseteli/handler/package.json
@@ -23,7 +23,7 @@
     "@sentry/nextjs": "^7.16.0",
     "axios": "^0.27.2",
     "dotenv": "^16.0.0",
-    "finnish-ssn": "2.0.4",
+    "finnish-ssn": "^2.1.2",
     "hds-design-tokens": "^2.17.0",
     "hds-react": "^2.17.0",
     "lodash": "^4.17.21",
diff --git a/frontend/kesaseteli/shared/package.json b/frontend/kesaseteli/shared/package.json
index 6c493e891d..964b0ef3af 100644
--- a/frontend/kesaseteli/shared/package.json
+++ b/frontend/kesaseteli/shared/package.json
@@ -15,7 +15,7 @@
   "dependencies": {
     "@frontend/shared": "*",
     "axios": "^0.27.2",
-    "finnish-ssn": "2.0.4",
+    "finnish-ssn": "^2.1.2",
     "react-query": "^3.34.0"
   },
   "devDependencies": {
diff --git a/frontend/kesaseteli/youth/package.json b/frontend/kesaseteli/youth/package.json
index cb403219d3..5ba8d14910 100644
--- a/frontend/kesaseteli/youth/package.json
+++ b/frontend/kesaseteli/youth/package.json
@@ -24,7 +24,7 @@
     "@sentry/nextjs": "^7.16.0",
     "axios": "^0.27.2",
     "dotenv": "^16.0.0",
-    "finnish-ssn": "2.0.4",
+    "finnish-ssn": "^2.1.2",
     "hds-design-tokens": "^2.17.0",
     "hds-react": "^2.17.0",
     "lodash": "^4.17.21",
diff --git a/frontend/shared/package.json b/frontend/shared/package.json
index 61c62080d2..7d1793449f 100644
--- a/frontend/shared/package.json
+++ b/frontend/shared/package.json
@@ -21,7 +21,7 @@
     "dotenv": "^16.0.0",
     "express": "^4.17.1",
     "fast-deep-equal": "^3.1.3",
-    "finnish-ssn": "^2.1.1",
+    "finnish-ssn": "^2.1.2",
     "hds-react": "^2.17.0",
     "js-file-download": "^0.4.12",
     "lodash": "^4.17.21",
diff --git a/frontend/shared/src/__tests__/constants.test.ts b/frontend/shared/src/__tests__/constants.test.ts
index 909a01241c..24ec09240c 100644
--- a/frontend/shared/src/__tests__/constants.test.ts
+++ b/frontend/shared/src/__tests__/constants.test.ts
@@ -4,6 +4,7 @@ import {
   ADDRESS_REGEX,
   CITY_REGEX,
   COMPANY_BANK_ACCOUNT_NUMBER,
+  FINNISH_SSN_REGEX,
   NAMES_REGEX,
   PHONE_NUMBER_REGEX,
   POSTAL_CODE_REGEX,
@@ -197,5 +198,97 @@ describe('constants', () => {
         expect(accountNumber).not.toMatch(COMPANY_BANK_ACCOUNT_NUMBER);
       });
     });
+
+    describe('FINNISH_SSN_REGEX', () => {
+      it('should match Finnish non-temporary social security numbers', () => {
+        const socialSecurityNumbers = [
+          '010100+002H',
+          '010203-1230',
+          '111111-002V',
+          '111111-111C',
+          '111111A111C',
+          '111111U111C',
+          '111111V111C',
+          '111111W111C',
+          '111111X111C',
+          '111111Y111C',
+          '121212A899H',
+          '121212B899H',
+          '121212C899H',
+          '121212D899H',
+          '121212E899H',
+          '121212F899H',
+          '300522A0024',
+          '300522B0024',
+          // All possible checksum characters & before first & beyond last
+          '111111B098Y',
+          '111111B0990',
+          '111111B1001',
+          '111111B1012',
+          '111111B1023',
+          '111111B1034',
+          '111111B1045',
+          '111111B1056',
+          '111111B1067',
+          '111111B1078',
+          '111111B1089',
+          '111111B109A',
+          '111111B110B',
+          '111111B111C',
+          '111111B112D',
+          '111111B113E',
+          '111111B114F',
+          '111111B115H',
+          '111111B116J',
+          '111111B117K',
+          '111111B118L',
+          '111111B119M',
+          '111111B120N',
+          '111111B121P',
+          '111111B122R',
+          '111111B123S',
+          '111111B124T',
+          '111111B125U',
+          '111111B126V',
+          '111111B127W',
+          '111111B128X',
+          '111111B129Y',
+          '111111B1300',
+        ];
+
+        socialSecurityNumbers.forEach((socialSecurityNumber) => {
+          expect(socialSecurityNumber).toMatch(FINNISH_SSN_REGEX);
+        });
+      });
+
+      it('should not match Finnish temporary or invalid social security numbers', () => {
+        const socialSecurityNumbers = [
+          '111111-900U', // Otherwise valid but 900–999 individual number is rejected
+          '111111-9991', // Otherwise valid but 900–999 individual number is rejected
+          '111111-900U', // Otherwise valid but 900–999 individual number is rejected
+          '111111-9991', // Otherwise valid but 900–999 individual number is rejected
+          '311299A999E', // Otherwise valid but 900–999 individual number is rejected
+          '311299F999E', // Otherwise valid but 900–999 individual number is rejected
+          '30052 2A0025', //  Inner whitespace
+          '111111 -111x', //  Invalid checksum, inner whitespace
+          '111111/111C', //  Invalid century character
+          '111111G111C', //  Invalid century character
+          '111111M111C', //  Invalid century character
+          '111111R111C', //  Invalid century character
+          '111111T111C', //  Invalid century character
+          '111111Z111C', //  Invalid century character
+          '111111B111G', // Invalid checksum character
+          '111111B111I', // Invalid checksum character
+          '111111B111O', // Invalid checksum character
+          '111111B111Q', // Invalid checksum character
+          '111111B111Z', // Invalid checksum character
+          '111111B111', // Missing checksum
+        ];
+
+        socialSecurityNumbers.forEach((socialSecurityNumber) => {
+          expect(socialSecurityNumber).not.toMatch(FINNISH_SSN_REGEX);
+        });
+      });
+    });
   });
 });
diff --git a/frontend/shared/src/constants.ts b/frontend/shared/src/constants.ts
index 969ca4ff8a..da33bec812 100644
--- a/frontend/shared/src/constants.ts
+++ b/frontend/shared/src/constants.ts
@@ -26,6 +26,6 @@ export const DATE_VTJ_REGEX = /^\d{4}(0?[1-9]|1[0-2])(0?[1-9]|[12]\d|3[01])$/;
 
 // a modification of finnish ssn regex https://regex101.com/library/HPFWw6 that does not accept "fake" (keinotunnus) ssn's:
 // https://www.tuomas.salste.net/doc/tunnus/henkilotunnus.html#keinotunnus (more info only in finnish)
-export const FINNISH_SSN_REGEX = /^\d{6}[+Aa-][0-8]\d{2}[\dA-z]$/;
+export const FINNISH_SSN_REGEX = /^\d{6}[+a-fu-y-][0-8]\d{2}[\da-fhj-npr-y]$/i;
 export const WEBSITE_URL =
   /(https?:\/\/(?:www\.|(?!www))[\da-z][\da-z-]+[\da-z]\.\S{2,}|www\.[\da-z][\da-z-]+[\da-z]\.\S{2,}|https?:\/\/(?:www\.|(?!www))[\da-z]+\.\S{2,}|www\.[\da-z]+\.\S{2,})/gi;
diff --git a/frontend/shared/src/utils/__tests__/mask-gdpr-data.test.ts b/frontend/shared/src/utils/__tests__/mask-gdpr-data.test.ts
index 8526afd9ad..c5adf0d335 100644
--- a/frontend/shared/src/utils/__tests__/mask-gdpr-data.test.ts
+++ b/frontend/shared/src/utils/__tests__/mask-gdpr-data.test.ts
@@ -8,6 +8,7 @@ import maskGDPRData from 'shared/utils/mask-gdpr-data';
 const fakeObjectFactory = new FakeObjectFactory({ useUuid: false });
 
 const masked = (str?: string): string => '*'.repeat(str?.length ?? 0);
+const MASKED_SSN = '***********' as const;
 
 describe('frontend/shared/src/utils/masked-gdpr-data.ts', () => {
   it('masks youth application', () => {
@@ -66,8 +67,13 @@ describe('frontend/shared/src/utils/masked-gdpr-data.ts', () => {
     );
     const text1 = faker.lorem.text();
     const text2 = faker.lorem.text();
-    expect(maskGDPRData(text1 + ssn + text2)).toEqual(
-      text1 + masked(ssn) + text2
+    const expectedResult = text1 + MASKED_SSN + text2;
+    expect(maskGDPRData(text1 + ssn + text2)).toEqual(expectedResult);
+    expect(maskGDPRData(text1 + ssn.toLowerCase() + text2)).toEqual(
+      expectedResult
+    );
+    expect(maskGDPRData(text1 + ssn.toUpperCase() + text2)).toEqual(
+      expectedResult
     );
   });
 
@@ -80,17 +86,30 @@ describe('frontend/shared/src/utils/masked-gdpr-data.ts', () => {
     );
     const text1 = faker.lorem.text();
     const text2 = faker.lorem.text();
-    const obj = {
-      foo: {
-        bar: text1 + ssn1 + text2,
-      },
-      baz: `${ssn1}0${ssn2}`,
+    const expectedResult = {
+      foo: { bar: text1 + MASKED_SSN + text2 },
+      baz: `${MASKED_SSN}0${MASKED_SSN}`,
     };
-    expect(maskGDPRData(obj)).toEqual({
-      foo: {
-        bar: text1 + masked(ssn1) + text2,
-      },
-      baz: `${masked(ssn1)}0${masked(ssn2)}`,
-    });
+
+    expect(
+      maskGDPRData({
+        foo: { bar: text1 + ssn1 + text2 },
+        baz: `${ssn1}0${ssn2}`,
+      })
+    ).toEqual(expectedResult);
+
+    expect(
+      maskGDPRData({
+        foo: { bar: text1 + ssn1.toLowerCase() + text2 },
+        baz: `${ssn1.toLowerCase()}0${ssn2.toLowerCase()}`,
+      })
+    ).toEqual(expectedResult);
+
+    expect(
+      maskGDPRData({
+        foo: { bar: text1 + ssn1.toUpperCase() + text2 },
+        baz: `${ssn1.toUpperCase()}0${ssn2.toUpperCase()}`,
+      })
+    ).toEqual(expectedResult);
   });
 });
diff --git a/frontend/shared/src/utils/mask-gdpr-data.ts b/frontend/shared/src/utils/mask-gdpr-data.ts
index 627decae93..c98c07bbb2 100644
--- a/frontend/shared/src/utils/mask-gdpr-data.ts
+++ b/frontend/shared/src/utils/mask-gdpr-data.ts
@@ -7,7 +7,7 @@ import { isString } from 'shared/utils/type-guards';
 
 const maskFinnishSsn = (text: unknown): unknown =>
   isString(text)
-    ? text.replace(/\d{6}[+-y]\d{3}[\dA-z]/g, '*'.repeat(11))
+    ? text.replace(/\d{6}[+a-z-]\d{3}[\da-z]/gi, '*'.repeat(11))
     : text;
 
 /* Gets the length of the given variable */
diff --git a/frontend/yarn.lock b/frontend/yarn.lock
index 74e86fd043..fb7caa8ece 100644
--- a/frontend/yarn.lock
+++ b/frontend/yarn.lock
@@ -7225,15 +7225,10 @@ finnish-business-ids@^3.1.1:
   resolved "https://registry.yarnpkg.com/finnish-business-ids/-/finnish-business-ids-3.1.1.tgz#cedde5d391bd290f9112e51d81cb2a340f4a7ee4"
   integrity sha512-9MbFNBoLas7BoYw+rtPYy0xTAtfE1ResD0CUMEZLXuSythlpThZjuBHF35ELNIMslSnZnHRVpzYKrQrf9buWSQ==
 
-finnish-ssn@2.0.4:
-  version "2.0.4"
-  resolved "https://registry.yarnpkg.com/finnish-ssn/-/finnish-ssn-2.0.4.tgz#5614b48b91ba63f4a27367971797291a47628d8c"
-  integrity sha512-boRI1T1W4Y+d6A8A5aujN7HJVE6HEXtXOevasvo8Xipi2gxcBKTSj07OWVoJl2bq4eBtH4drh2UgNMnQpHIJ+A==
-
-finnish-ssn@^2.1.1:
-  version "2.1.1"
-  resolved "https://registry.yarnpkg.com/finnish-ssn/-/finnish-ssn-2.1.1.tgz#0f0685666530ddc4c36a0c0d34d0ba0c413d7cb2"
-  integrity sha512-0mwAfmHw2PlSZ+niAWNtYvzw+byG881qSIN9sWZRadxE3CW8KdtIYlfwvk0J7MzlnrE7HM19DM78LJrt7X1PvQ==
+finnish-ssn@^2.1.2:
+  version "2.1.2"
+  resolved "https://registry.yarnpkg.com/finnish-ssn/-/finnish-ssn-2.1.2.tgz#5fa8d42a42fe7b3de214240c7dd373f3b18fda3f"
+  integrity sha512-B8xXx9KNnwG0l0wUkz6OtctYs/ffTlvVcbj4W1qFMgI/YyB5XCjEqTcbZ3ZK0tgOourb54CSZAenQQQNVxzBMA==
 
 flat-cache@^3.0.4:
   version "3.0.4"