diff --git a/README.md b/README.md
index f1ca56ee..e78baed6 100644
--- a/README.md
+++ b/README.md
@@ -65,13 +65,13 @@ Format: `help`
 #### Adding a person: `add`
 > Adds a person to the address book
 
-Format: `add NAME p/PHONE_NUMBER e/EMAIL`  
+Format: `add NAME p/PHONE_NUMBER e/EMAIL c/POSTAL_CODE`
 > Words in `UPPER_CASE` are the parameters<br>
   Phone number and email can be in any order but the name must come first.
 
 Examples: 
-* `add John Doe p/98765432 e/johnd@gmail.com`
-* `add Betsy Crowe e/bencrowe@gmail.com p/1234567 `
+* `add John Doe p/98765432 e/johnd@gmail.com c/123456`
+* `add Betsy Crowe e/bencrowe@gmail.com p/1234567 c/111111`
 
 #### Listing all persons: `list`
 
diff --git a/src/seedu/addressbook/AddressBook.java b/src/seedu/addressbook/AddressBook.java
index 5a158b67..c904bdfd 100644
--- a/src/seedu/addressbook/AddressBook.java
+++ b/src/seedu/addressbook/AddressBook.java
@@ -65,13 +65,13 @@ public class AddressBook {
      * at which java String.format(...) method can insert values.
      * =========================================================================
      */
-    private static final String MESSAGE_ADDED = "New person added: %1$s, Phone: %2$s, Email: %3$s";
+    private static final String MESSAGE_ADDED = "New person added: %1$s, Phone: %2$s, Email: %3$s, Postal Code: %4$s";
     private static final String MESSAGE_ADDRESSBOOK_CLEARED = "Address book has been cleared!";
     private static final String MESSAGE_COMMAND_HELP = "%1$s: %2$s";
     private static final String MESSAGE_COMMAND_HELP_PARAMETERS = "\tParameters: %1$s";
     private static final String MESSAGE_COMMAND_HELP_EXAMPLE = "\tExample: %1$s";
     private static final String MESSAGE_DELETE_PERSON_SUCCESS = "Deleted Person: %1$s";
-    private static final String MESSAGE_DISPLAY_PERSON_DATA = "%1$s  Phone Number: %2$s  Email: %3$s";
+    private static final String MESSAGE_DISPLAY_PERSON_DATA = "%1$s  Phone Number: %2$s  Email: %3$s Postal Code: %4$s";
     private static final String MESSAGE_DISPLAY_LIST_ELEMENT_INDEX = "%1$d. ";
     private static final String MESSAGE_GOODBYE = "Exiting Address Book... Good bye!";
     private static final String MESSAGE_INVALID_COMMAND_FORMAT = "Invalid command format: %1$s " + LS + "%2$s";
@@ -94,16 +94,21 @@ public class AddressBook {
     // These are the prefix strings to define the data type of a command parameter
     private static final String PERSON_DATA_PREFIX_PHONE = "p/";
     private static final String PERSON_DATA_PREFIX_EMAIL = "e/";
+    private static final String PERSON_DATA_PREFIX_POSTALCODE = "c/";
 
     private static final String PERSON_STRING_REPRESENTATION = "%1$s " // name
                                                             + PERSON_DATA_PREFIX_PHONE + "%2$s " // phone
-                                                            + PERSON_DATA_PREFIX_EMAIL + "%3$s"; // email
+                                                            + PERSON_DATA_PREFIX_EMAIL + "%3$s " // email
+                                                            + PERSON_DATA_PREFIX_POSTALCODE + "%4$s"; // postal code
     private static final String COMMAND_ADD_WORD = "add";
     private static final String COMMAND_ADD_DESC = "Adds a person to the address book.";
     private static final String COMMAND_ADD_PARAMETERS = "NAME "
                                                       + PERSON_DATA_PREFIX_PHONE + "PHONE_NUMBER "
-                                                      + PERSON_DATA_PREFIX_EMAIL + "EMAIL";
-    private static final String COMMAND_ADD_EXAMPLE = COMMAND_ADD_WORD + " John Doe p/98765432 e/johnd@gmail.com";
+                                                      + PERSON_DATA_PREFIX_EMAIL + "EMAIL "
+                                                      + PERSON_DATA_PREFIX_POSTALCODE + "POSTAL_CODE";
+
+    private static final String COMMAND_ADD_EXAMPLE = COMMAND_ADD_WORD +
+                                                      " John Doe p/98765432 e/johnd@gmail.com c/123456";
 
     private static final String COMMAND_FIND_WORD = "find";
     private static final String COMMAND_FIND_DESC = "Finds all persons whose names contain any of the specified "
@@ -144,11 +149,13 @@ public class AddressBook {
     private static final int PERSON_DATA_INDEX_NAME = 0;
     private static final int PERSON_DATA_INDEX_PHONE = 1;
     private static final int PERSON_DATA_INDEX_EMAIL = 2;
+    private static final int PERSON_DATA_INDEX_POSTALCODE = 3;
+
 
     /**
      * The number of data elements for a single person.
      */
-    private static final int PERSON_DATA_COUNT = 3;
+    private static final int PERSON_DATA_COUNT = 4;
 
     /**
      * Offset required to convert between 1-indexing and 0-indexing.COMMAND_
@@ -439,7 +446,8 @@ private static String executeAddPerson(String commandArgs) {
      */
     private static String getMessageForSuccessfulAddPerson(String[] addedPerson) {
         return String.format(MESSAGE_ADDED,
-                getNameFromPerson(addedPerson), getPhoneFromPerson(addedPerson), getEmailFromPerson(addedPerson));
+                getNameFromPerson(addedPerson), getPhoneFromPerson(addedPerson),
+                getEmailFromPerson(addedPerson), getPostalFromPerson(addedPerson));
     }
 
     /**
@@ -669,7 +677,8 @@ private static String getIndexedPersonListElementMessage(int visibleIndex, Strin
      */
     private static String getMessageForFormattedPersonData(String[] person) {
         return String.format(MESSAGE_DISPLAY_PERSON_DATA,
-                getNameFromPerson(person), getPhoneFromPerson(person), getEmailFromPerson(person));
+                getNameFromPerson(person), getPhoneFromPerson(person),
+                getEmailFromPerson(person), getPostalFromPerson(person));
     }
 
     /**
@@ -860,6 +869,15 @@ private static String getEmailFromPerson(String[] person) {
         return person[PERSON_DATA_INDEX_EMAIL];
     }
 
+    /**
+     * Returns given person's postal code
+     *
+     * @param person whose postal code you want
+     */
+    private static String getPostalFromPerson(String[] person) {
+        return person[PERSON_DATA_INDEX_POSTALCODE];
+    }
+
     /**
      * Creates a person from the given data.
      *
@@ -868,11 +886,12 @@ private static String getEmailFromPerson(String[] person) {
      * @param email without data prefix
      * @return constructed person
      */
-    private static String[] makePersonFromData(String name, String phone, String email) {
+    private static String[] makePersonFromData(String name, String phone, String email, String postalCode) {
         final String[] person = new String[PERSON_DATA_COUNT];
         person[PERSON_DATA_INDEX_NAME] = name;
         person[PERSON_DATA_INDEX_PHONE] = phone;
         person[PERSON_DATA_INDEX_EMAIL] = email;
+        person[PERSON_DATA_INDEX_POSTALCODE] = postalCode;
         return person;
     }
 
@@ -884,7 +903,8 @@ private static String[] makePersonFromData(String name, String phone, String ema
      */
     private static String encodePersonToString(String[] person) {
         return String.format(PERSON_STRING_REPRESENTATION,
-                getNameFromPerson(person), getPhoneFromPerson(person), getEmailFromPerson(person));
+                getNameFromPerson(person), getPhoneFromPerson(person),
+                getEmailFromPerson(person), getPostalFromPerson(person));
     }
 
     /**
@@ -923,7 +943,9 @@ private static Optional<String[]> decodePersonFromString(String encoded) {
         final String[] decodedPerson = makePersonFromData(
                 extractNameFromPersonString(encoded),
                 extractPhoneFromPersonString(encoded),
-                extractEmailFromPersonString(encoded)
+                extractEmailFromPersonString(encoded),
+                extractPostalFromPersonString(encoded)
+
         );
         // check that the constructed person is valid
         return isPersonDataValid(decodedPerson) ? Optional.of(decodedPerson) : Optional.empty();
@@ -955,12 +977,15 @@ private static Optional<ArrayList<String[]>> decodePersonsFromStrings(ArrayList<
      * @param personData person string representation
      */
     private static boolean isPersonDataExtractableFrom(String personData) {
-        final String matchAnyPersonDataPrefix = PERSON_DATA_PREFIX_PHONE + '|' + PERSON_DATA_PREFIX_EMAIL;
+        final String matchAnyPersonDataPrefix = PERSON_DATA_PREFIX_PHONE + '|' +
+                                                PERSON_DATA_PREFIX_EMAIL+ '|' +
+                                                PERSON_DATA_PREFIX_POSTALCODE;
         final String[] splitArgs = personData.trim().split(matchAnyPersonDataPrefix);
-        return splitArgs.length == 3 // 3 arguments
+        return splitArgs.length == 4 // 4 arguments
                 && !splitArgs[0].isEmpty() // non-empty arguments
                 && !splitArgs[1].isEmpty()
-                && !splitArgs[2].isEmpty();
+                && !splitArgs[2].isEmpty()
+                && !splitArgs[3].isEmpty();
     }
 
     /**
@@ -986,17 +1011,24 @@ private static String extractNameFromPersonString(String encoded) {
     private static String extractPhoneFromPersonString(String encoded) {
         final int indexOfPhonePrefix = encoded.indexOf(PERSON_DATA_PREFIX_PHONE);
         final int indexOfEmailPrefix = encoded.indexOf(PERSON_DATA_PREFIX_EMAIL);
+        final int indexOfPostalPrefix = encoded.indexOf(PERSON_DATA_PREFIX_POSTALCODE);
 
         // phone is last arg, target is from prefix to end of string
-        if (indexOfPhonePrefix > indexOfEmailPrefix) {
+        if (indexOfPhonePrefix > indexOfEmailPrefix  && indexOfPhonePrefix > indexOfPostalPrefix) {
             return removePrefixSign(encoded.substring(indexOfPhonePrefix, encoded.length()).trim(),
                     PERSON_DATA_PREFIX_PHONE);
 
-        // phone is middle arg, target is from own prefix to next prefix
-        } else {
+        // phone is before mail, target is from own prefix to next prefix
+        } else if ((indexOfPhonePrefix < indexOfEmailPrefix && indexOfPostalPrefix < indexOfPhonePrefix)
+                    || (indexOfPhonePrefix < indexOfEmailPrefix && indexOfPostalPrefix > indexOfPhonePrefix)) {
             return removePrefixSign(
                     encoded.substring(indexOfPhonePrefix, indexOfEmailPrefix).trim(),
                     PERSON_DATA_PREFIX_PHONE);
+            // phone is before postal code, target is from own prefix to next prefix
+        } else {
+            return removePrefixSign(
+                    encoded.substring(indexOfPhonePrefix, indexOfPostalPrefix).trim(),
+                    PERSON_DATA_PREFIX_PHONE);
         }
     }
 
@@ -1008,30 +1040,70 @@ private static String extractPhoneFromPersonString(String encoded) {
      */
     private static String extractEmailFromPersonString(String encoded) {
         final int indexOfPhonePrefix = encoded.indexOf(PERSON_DATA_PREFIX_PHONE);
+        final int indexOfPostalPrefix = encoded.indexOf(PERSON_DATA_PREFIX_POSTALCODE);
         final int indexOfEmailPrefix = encoded.indexOf(PERSON_DATA_PREFIX_EMAIL);
 
         // email is last arg, target is from prefix to end of string
-        if (indexOfEmailPrefix > indexOfPhonePrefix) {
+        if (indexOfEmailPrefix > indexOfPhonePrefix && indexOfEmailPrefix > indexOfPostalPrefix) {
             return removePrefixSign(encoded.substring(indexOfEmailPrefix, encoded.length()).trim(),
                     PERSON_DATA_PREFIX_EMAIL);
 
-        // email is middle arg, target is from own prefix to next prefix
+        // email is before postal code, target is from own prefix to next prefix
+        } else if ((indexOfEmailPrefix > indexOfPhonePrefix && indexOfEmailPrefix < indexOfPostalPrefix)
+                    || (indexOfEmailPrefix < indexOfPhonePrefix && indexOfEmailPrefix < indexOfPostalPrefix)){
+            return removePrefixSign(
+                    encoded.substring(indexOfEmailPrefix, indexOfPostalPrefix).trim(),
+                    PERSON_DATA_PREFIX_EMAIL);
+        // email is middle arg, phone is last arg, target is from own prefix to next prefix
         } else {
             return removePrefixSign(
-                    encoded.substring(indexOfEmailPrefix, indexOfPhonePrefix).trim(),
+                    encoded.substring(indexOfPhonePrefix, indexOfEmailPrefix).trim(),
                     PERSON_DATA_PREFIX_EMAIL);
         }
     }
 
+
+    /**
+     * Extracts substring representing postal code from person string representation
+     *
+     * @param encoded person string representation
+     * @return postal code argument WITHOUT prefix
+     */
+    private static String extractPostalFromPersonString(String encoded) {
+        final int indexOfPhonePrefix = encoded.indexOf(PERSON_DATA_PREFIX_PHONE);
+        final int indexOfPostalPrefix = encoded.indexOf(PERSON_DATA_PREFIX_POSTALCODE);
+        final int indexOfEmailPrefix = encoded.indexOf(PERSON_DATA_PREFIX_EMAIL);
+
+        // pc is last arg, target is from prefix to end of string
+        if (indexOfPostalPrefix > indexOfEmailPrefix  && indexOfPostalPrefix > indexOfPhonePrefix) {
+            return removePrefixSign(encoded.substring(indexOfPostalPrefix, encoded.length()).trim(),
+                    PERSON_DATA_PREFIX_POSTALCODE);
+
+            // pc is before email target is from own prefix to next prefix
+        } else if ((indexOfPostalPrefix < indexOfEmailPrefix && indexOfPhonePrefix < indexOfPostalPrefix)
+                    || (indexOfPostalPrefix < indexOfEmailPrefix && indexOfPhonePrefix > indexOfPostalPrefix)){
+            return removePrefixSign(
+                    encoded.substring(indexOfPostalPrefix, indexOfEmailPrefix).trim(),
+                    PERSON_DATA_PREFIX_POSTALCODE);
+
+            // pc is middle arg, phone is last arg, target is from own prefix to next prefix
+        } else {
+            return removePrefixSign(
+                    encoded.substring(indexOfPostalPrefix, indexOfPhonePrefix).trim(),
+                    PERSON_DATA_PREFIX_POSTALCODE);
+        }
+    }
+
     /**
      * Returns true if the given person's data fields are valid
      *
      * @param person String array representing the person (used in internal data)
      */
     private static boolean isPersonDataValid(String[] person) {
-        return isPersonNameValid(person[PERSON_DATA_INDEX_NAME])
-                && isPersonPhoneValid(person[PERSON_DATA_INDEX_PHONE])
-                && isPersonEmailValid(person[PERSON_DATA_INDEX_EMAIL]);
+        return isPersonNameValid(person[PERSON_DATA_INDEX_NAME], "(\\w|\\s)+")
+                && isPersonPhoneValid(person[PERSON_DATA_INDEX_PHONE], "\\d+")
+                && isPersonEmailValid(person[PERSON_DATA_INDEX_EMAIL], "\\S+@\\S+\\.\\S+")
+                && isPersonPostalValid(person[PERSON_DATA_INDEX_POSTALCODE], "\\d+");
     }
 
     /*
@@ -1046,9 +1118,10 @@ && isPersonPhoneValid(person[PERSON_DATA_INDEX_PHONE])
      * Returns true if the given string as a legal person name
      *
      * @param name to be validated
+     * @param regex
      */
-    private static boolean isPersonNameValid(String name) {
-        return name.matches("(\\w|\\s)+");  // name is nonempty mixture of alphabets and whitespace
+    private static boolean isPersonNameValid(String name, String regex) {
+        return isPersonPhoneValid(name, regex);  // name is nonempty mixture of alphabets and whitespace
         //TODO: implement a more permissive validation
     }
 
@@ -1056,9 +1129,10 @@ private static boolean isPersonNameValid(String name) {
      * Returns true if the given string as a legal person phone number
      *
      * @param phone to be validated
+     * @param regex
      */
-    private static boolean isPersonPhoneValid(String phone) {
-        return phone.matches("\\d+");    // phone nonempty sequence of digits
+    private static boolean isPersonPhoneValid(String phone, String regex) {
+        return phone.matches(regex);    // phone nonempty sequence of digits
         //TODO: implement a more permissive validation
     }
 
@@ -1066,13 +1140,25 @@ private static boolean isPersonPhoneValid(String phone) {
      * Returns true if the given string is a legal person email
      *
      * @param email to be validated
+     * @param regex
      * @return whether arg is a valid person email
      */
-    private static boolean isPersonEmailValid(String email) {
-        return email.matches("\\S+@\\S+\\.\\S+"); // email is [non-whitespace]@[non-whitespace].[non-whitespace]
+    private static boolean isPersonEmailValid(String email, String regex) {
+        return isPersonPhoneValid(email, regex); // email is [non-whitespace]@[non-whitespace].[non-whitespace]
         //TODO: implement a more permissive validation
     }
 
+    /**
+     * Returns true if the given string is a legal postal code
+     *
+     * @param postalCode to be validated
+     * @param regex
+     * @return whether arg is a legal postal code
+     */
+    private static boolean isPersonPostalValid(String postalCode, String regex) {
+        return isPersonPhoneValid(postalCode, regex); // email is [non-whitespace]@[non-whitespace].[non-whitespace]
+        //TODO: implement a more permissive validation
+    }
 
     /*
      * ===============================================
diff --git a/test/input.txt b/test/input.txt
index 0b99df54..dcbb227a 100644
--- a/test/input.txt
+++ b/test/input.txt
@@ -19,26 +19,27 @@
 
   # should catch invalid args format
   add wrong args wrong args
-  add Valid Name p/12345 valid@email.butNoPrefix
-  add Valid Name 12345 e/valid@email.butPhonePrefixMissing
+  add Valid Name p/12345 valid@email.butNoPrefix c/111111
+  add Valid Name 12345 e/valid@email.butPhonePrefixMissing c/111111
   
   # should catch invalid person data
   add []\[;] p/12345 e/valid@e.mail
-  add Valid Name p/not_numbers e/valid@e.mail
-  add Valid Name p/12345 e/notAnEmail
+  add Valid Name p/not_numbers e/valid@e.mail c/111111
+  add Valid Name p/12345 e/notAnEmail c/111111
+  add Valid Name p/12345 e/valid@e.mail c/not_numbers
 
   # should add correctly
-  add Adam Brown p/111111 e/adam@gmail.com
+  add Adam Brown p/111111 e/adam@gmail.com c/111111
   list
-  add Betsy Choo p/222222 e/benchoo@nus.edu.sg
+  add Betsy Choo p/222222 e/benchoo@nus.edu.sg c/222222
   list
 
-  # order of phone and email should not matter
-  add Charlie Dickson e/charlie.d@nus.edu.sg p/333333
+  # order of phone and email and postal code should not matter
+  add Charlie Dickson e/charlie.d@nus.edu.sg p/333333 c/111111
   list
-  add Dickson Ee e/dickson@nus.edu.sg p/444444
+  add Dickson Ee e/dickson@nus.edu.sg p/444444 c/111111
   list
-  add Esther Potato p/555555 e/esther@notreal.potato
+  add Esther Potato p/555555 c/111111 e/esther@notreal.potato
   list
 
 ##########################################################