How is the PPSN first check character calculated?

Multiply digit 1 by 8, digit 2 by 7, digit 3 by 6, digit 4 by 5, digit 5 by 4, digit 6 by 3 and digit 7 by 2. Sum all seven products. Take the result modulo 23. A remainder of 0 maps to W; remainders 1 to 22 map to A through V in alphabetical order. The letter at that position must equal the 8th character of the PPSN.

What is the second check character in new-format PPSNs?

Numbers issued from 2013 onward carry a W at position 8 and a second check character at position 9. The second character is computed with different weights (7,5,8,3,2,9,4 for digits 1-7) using the same modulo-23 alphabet. W in position 8 signals the presence of this second check, making the number 9 characters in total.

Does a valid result mean the PPSN really exists?

No. The tool confirms the format and modulo-23 arithmetic are correct, but it never queries any government register. A structurally valid PPSN may not have been issued to a real person. Only the Department of Social Protection can confirm assignment.

What embedded information does a PPSN contain?

Unlike some other national identifiers, a PPS number encodes no birth date, gender or region. The seven digits are a plain sequential serial number assigned by the DSP. The check character(s) are the only structured component — there is nothing else to decode.

What is the difference between old-format and new-format PPSNs?

Old-format numbers are 8 characters long (7 digits plus one check letter A-V). New-format numbers introduced around 2013 are 9 characters long (7 digits, W at position 8 as a format flag, and a second check letter A-V). The W in position 8 is not itself a checksum result in new-format numbers — it is a structural indicator.

Is my PPS number sent anywhere?

No. The entire validation runs inside your browser using JavaScript. No data is transmitted to any server, and nothing is logged or stored. You can disconnect from the internet and the tool will still work.

Ireland PPS Number Validator

An Irish PPS Number (Personal Public Service Number, commonly written PPSN) is the unique identifier issued by the Department of Social Protection (DSP) for every individual engaging with Irish public services — from filing a tax return with Revenue to accessing social welfare payments, applying for a driving licence or enrolling a child in school. Data-entry errors are common because the number looks like a simple alphanumeric string, but it carries a carefully designed check character that catches most single-character mistakes. This tool validates a PPSN by running the full modulo-23 algorithm and showing you the step-by-step arithmetic, so you can see exactly why a number passes or fails rather than just receiving a yes-or-no answer.

Format overview

A PPS number consists of three parts:

7 numeric digits — a plain sequential serial number with no encoded birth date, gender or region. The digits are simply the next available number in the DSP’s sequence.
First check character (position 8) — a letter from A to W computed by the mod-23 algorithm described below.
Optional second check character (position 9, new-format only) — present only on numbers issued or re-issued from around 2013 onward. When a second check character exists, position 8 is always W (acting as a format flag rather than a checksum result).

Old-format numbers are 8 characters (e.g. 1234567T). New-format numbers are 9 characters (e.g. 1234567WB). Both formats remain in active circulation.

The modulo-23 algorithm explained

First check character (applies to all PPSNs):

Digit position	1	2	3	4	5	6	7
Weight	8	7	6	5	4	3	2

Multiply each digit by its weight and sum all seven products. Divide the sum by 23 and keep the remainder. Map that remainder to a letter using this table:

Remainder	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22
Letter	W	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	P	Q	R	S	T	U	V

That mapped letter must equal position 8 of the PPSN.

Second check character (new-format 9-character numbers only):

The same seven digits are reweighted differently:

Digit position	1	2	3	4	5	6	7
Weight	7	5	8	3	2	9	4

Again sum the weighted products, mod 23, and map to the same letter table. The result must equal position 9 of the PPSN.

Worked example (obviously fictitious numbers only)

Take the fake number 1234567T (old format):

Weighted sum: (1×8) + (2×7) + (3×6) + (4×5) + (5×4) + (6×3) + (7×2) = 8 + 14 + 18 + 20 + 20 + 18 + 14 = 112
112 mod 23 = 20
Remainder 20 maps to T in the table above

So 1234567T has a correct check character. The tool performs this working and displays every intermediate value so you can verify it independently.

Every calculation runs locally in your browser. No PPSN you enter is ever transmitted, stored or logged.