diff --git a/CHANGELOG.md b/CHANGELOG.md
index a566449..421e4bf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,9 +10,10 @@ Updates should follow the [Keep a CHANGELOG](http://keepachangelog.com/) princip
 - Date formatters for formatting dates. Date formatters can be chained with word formatters. The output from the date formatter is used as input for the next formatter in the chain.
 - Date formatter combining the results from multiple date formatters.
 - Default date formatter.
+- Possible to specify date formatter for guessable data rules.
 
 ### Changed
-- Nothing
+- Constraint weight for guessable data rules is now argument number 4 instead of number 3. Date formatter is argument number 3.
 
 ### Fixed
 - Nothing
diff --git a/src/Rule/GuessableDataRule.php b/src/Rule/GuessableDataRule.php
index 5556565..8517a13 100644
--- a/src/Rule/GuessableDataRule.php
+++ b/src/Rule/GuessableDataRule.php
@@ -5,6 +5,8 @@
 namespace Stadly\PasswordPolice\Rule;
 
 use DateTimeInterface;
+use Stadly\PasswordPolice\DateFormatter;
+use Stadly\PasswordPolice\DateFormatter\DefaultFormatter;
 use Stadly\PasswordPolice\Password;
 use Stadly\PasswordPolice\Policy;
 use Stadly\PasswordPolice\Rule;
@@ -15,47 +17,6 @@
 
 final class GuessableDataRule implements Rule
 {
-    private const DATE_FORMATS = [
-        // Year
-        ['Y'], // 2018
-
-        // Year month
-        ['y', 'n'], // 18 8
-        ['y', 'm'], // 18 08
-        ['y', 'M'], // 18 Aug
-        ['y', 'F'], // 18 August
-
-        // Month year
-        ['n', 'y'], // 8 18
-        ['M', 'y'], // Aug 18
-        ['F', 'y'], // August 18
-
-        // Day month
-        ['j', 'n'], // 4 8
-        ['j', 'm'], // 4 08
-        ['j', 'M'], // 4 Aug
-        ['j', 'F'], // 4 August
-
-        // Month day
-        ['n', 'j'], // 8 4
-        ['n', 'd'], // 8 04
-        ['M', 'j'], // Aug 4
-        ['M', 'd'], // Aug 04
-        ['F', 'j'], // August 4
-        ['F', 'd'], // August 04
-    ];
-
-    private const DATE_SEPARATORS = [
-        '',
-        '-',
-        ' ',
-        '/',
-        '.',
-        ',',
-        '. ',
-        ', ',
-    ];
-
     /**
      * @var (string|DateTimeInterface)[] Guessable data.
      */
@@ -66,6 +27,11 @@ final class GuessableDataRule implements Rule
      */
     private $wordFormatter;
 
+    /**
+     * @var DateFormatter Date formatter.
+     */
+    private $dateFormatter;
+
     /**
      * @var int Constraint weight.
      */
@@ -74,12 +40,18 @@ final class GuessableDataRule implements Rule
     /**
      * @param (string|DateTimeInterface)[] $guessableData Guessable data.
      * @param WordFormatter[] $wordFormatters Word formatters.
+     * @param DateFormatter|null $dateFormatter Date formatter.
      * @param int $weight Constraint weight.
      */
-    public function __construct(array $guessableData = [], array $wordFormatters = [], int $weight = 1)
-    {
+    public function __construct(
+        array $guessableData = [],
+        array $wordFormatters = [],
+        ?DateFormatter $dateFormatter = null,
+        int $weight = 1
+    ) {
         $this->guessableData = $guessableData;
         $this->wordFormatter = new FormatterCombiner($wordFormatters);
+        $this->dateFormatter = $dateFormatter ?? new DefaultFormatter();
         $this->weight = $weight;
     }
 
@@ -153,31 +125,13 @@ private function getGuessableData($password)
     private function contains(string $password, $data): bool
     {
         if ($data instanceof DateTimeInterface) {
-            return $this->containsDate($password, $data);
+            $strings = $this->dateFormatter->apply([$data]);
+        } else {
+            $strings = [$data];
         }
 
-        return $this->containsString($password, $data);
-    }
-
-    /**
-     * @param string $password Password to check.
-     * @param string $string String to check.
-     * @return bool Whether the password contains the string.
-     */
-    private function containsString(string $password, string $string): bool
-    {
-        return mb_stripos($password, $string) !== false;
-    }
-
-    /**
-     * @param string $password Password to check.
-     * @param DateTimeInterface $date Date to check.
-     * @return bool Whether the password contains the date.
-     */
-    private function containsDate(string $password, DateTimeInterface $date): bool
-    {
-        foreach ($this->getDateFormats() as $format) {
-            if ($this->containsString($password, $date->format($format))) {
+        foreach ($strings as $string) {
+            if (mb_stripos($password, $string) !== false) {
                 return true;
             }
         }
@@ -185,18 +139,6 @@ private function containsDate(string $password, DateTimeInterface $date): bool
         return false;
     }
 
-    /**
-     * @return iterable<string> Date formats.
-     */
-    private function getDateFormats(): iterable
-    {
-        foreach (self::DATE_FORMATS as $format) {
-            foreach (self::DATE_SEPARATORS as $separator) {
-                yield implode($separator, $format);
-            }
-        }
-    }
-
     /**
      * @param string|DateTimeInterface $data Data that violates the constraint.
      * @return string Message explaining the violation.
diff --git a/tests/Rule/GuessableDataRuleTest.php b/tests/Rule/GuessableDataRuleTest.php
index d373c0a..a630ded 100644
--- a/tests/Rule/GuessableDataRuleTest.php
+++ b/tests/Rule/GuessableDataRuleTest.php
@@ -6,6 +6,7 @@
 
 use DateTime;
 use PHPUnit\Framework\TestCase;
+use Stadly\PasswordPolice\DateFormatter;
 use Stadly\PasswordPolice\Password;
 use Stadly\PasswordPolice\ValidationError;
 use Stadly\PasswordPolice\WordFormatter;
@@ -111,7 +112,7 @@ public function testPasswordCanNotContainGuessableDate(): void
      */
     public function testRuleIsSatisfiedWhenConstraintWeightIsLowerThanTestWeight(): void
     {
-        $rule = new GuessableDataRule([], [], 1);
+        $rule = new GuessableDataRule([], [], null, 1);
         $password = new Password('foobar', ['oba']);
 
         self::assertTrue($rule->test($password, 2));
@@ -237,6 +238,26 @@ static function (iterable $words): Traversable {
         self::assertFalse($rule->test(new Password('apple', ['fpple'])));
     }
 
+    /**
+     * @covers ::test
+     */
+    public function testDateFormatterCanBeCustomized(): void
+    {
+        $dateFormatter = $this->createMock(DateFormatter::class);
+        $dateFormatter->method('apply')->willReturnCallback(
+            static function (iterable $dates): Traversable {
+                foreach ($dates as $date) {
+                    yield $date->format('m\o\n\t\h');
+                }
+            }
+        );
+
+        $rule = new GuessableDataRule([], [], $dateFormatter);
+
+        self::assertFalse($rule->test(new Password('test 11onth foo', [new DateTime('2018-11-28')])));
+        self::assertTrue($rule->test(new Password('2018-11-28', [new DateTime('2018-11-28')])));
+    }
+
     /**
      * @covers ::validate
      */