# Does a PPS Number have any meaning?



## ajapale (16 May 2006)

Our payroll system "validates" PPS numbers but Im not sure on what basis it does this.

Does anyone know whether there is any meaning embedded in the pps number such as DOB etc.?


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## MugsGame (16 May 2006)

Seven digits plus one letter seems to be standard. In my case the letter is the first letter of my surname, but that may be a coincidence. There is probably a "check digit" to detect typing errors (similar to the Luhn code used for credit card numbers.). I doubt any useful information is encoded.


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## z107 (16 May 2006)

Yes, I can confirm that the letter at the end is a check digit. It is coincidence that it's also the first letter of the individual's name.

Some PPS numbers also have an additional letter for certain circumstances, like people who are married.


www.payback.ie


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## mf1 (16 May 2006)

I can remember when lodging Deeds for stamping in the Revenue in Dublin Castle  a few years ago, the guy behind the counter being able to tell me the approximate age group of my purchasers from the PPS - so I suspect that there is embedded info there. 

mf


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## ClubMan (16 May 2006)

I can find no evidence to support the claim that _PPSNs _encode any personal details and are anything other than a unique ID for an individual.


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## Howitzer (16 May 2006)

The numbers are random, the letter is arrived at using a Mod calculation. 

Back in the day all women used to have the same PPSN as their husbands with a W appended but once they started giving everyone a PPSN from an early age this was abandoned. If you have a W at the end now it means it got your PPSN a long time ago so your man in the queue may indeed have been able to guess the age range.

-- Amended post to remove the Mod number as it somewhat makes the validation on the OPs payrole system useless once you're able to make up valid PPSNs.


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## ajapale (16 May 2006)

A small proportion of PPS numbers have nine digits. These numbers relate to females and the last two characters are letters.

Im inclined to agree with Clubman as I have been unable to find evidence of any embedded intellegence in the PPS No.

Having said that it might be possible to deduce that any individual having a nine character pps number is female?

aj


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## ajapale (16 May 2006)

Thanks Howitzer, our posts crossed!

What is a 'mod caluclation'?


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## ClubMan (16 May 2006)

.


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## Howitzer (16 May 2006)

Crank up excel and look up the Maths functions. You're basically adding/multipying up the digits into a large number, dividing them by the Mod number and using the remainder to represent a letter of the alphabet (5 left over means E)

In fact revenue provide a document [broken link removed]


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## MugsGame (16 May 2006)

If numbers are released pseudo-sequentially, that would give another indication of the age of a person, without the age being encoded in the PPSN.


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## ClubMan (16 May 2006)

Not sure what you mean by "pseudo sequentially" but I don't think that anything can be inferred from the number itself. For example my 8 month old son received his _PPSN _soon after his birth last September. An adult worker could have received the next sequential _PPSN_. To infer that a "later" _PPSN_ indicates a younger person would be incorrect.


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## MugsGame (16 May 2006)

I'm trying to explain how mf1's anecdote above might arise without the age being encoded in the number. Particular tranches of numbers may have been used in particular years. If you know roughly what year the number was assigned, the person must have been born before then, so you have a lower bound on their age. Until recently numbers were typically assigned when people entered the workforce / claimed social welfare, which would allow you to narrow down the age range even further.

As you point out this won't generalise, e.g. because numbers are now assigned at birth, non-nationals get numbers when they enter the country etc. But as I said, it's only an indication.


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## ClubMan (16 May 2006)

Maybe the official in _mf1's_ case simply looked the _PPSNs _up on the computer? He really should not have been divulging any information about the people involved as far as I know.


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## porterbray (17 May 2006)

Yes there's modulus checksum used to verify that the number used is correct. Numbers for tax purposes were originally issued sequentially and so any number beginning with 0 or 1 would generally have been older taxpayers. Numbers beginning with 6 were often issued to people born in the 70's and early 80's. It is not as clearcut now as numbers never issued in the first place are being issued to new applicants.


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## Howitzer (17 May 2006)

porterbray said:
			
		

> It is not as clearcut now as numbers never issued in the first place are being issued to new applicants.


 
By my calculations there are only 9,999,999 (10 million) possible PPSN combinations (don't count the letter as it's simply a checksum to verify a valid number). With a current population of over 5 million, and assuming old numbers can't be re-issued, can anyone see a problem here?


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## MugsGame (17 May 2006)

Yes, particularly as numbers allocated to those who are now dead (not counted in the 5m) can't be recycled, at least not immediately. Worse still, I suspect Employer IDs (also 7 digits and a letter) come out of the same pool.


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## ClubMan (17 May 2006)

Isn't the _PPSN _a cradle to the grave number so that the limited range only becomes an issue if/when the population of the country nears 10 million? I presume that when  the individual's _PPSN _is eventually recycled?


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## Howitzer (17 May 2006)

ClubMan said:
			
		

> Isn't the _PPSN _a cradle to the grave number so that the limited range only becomes an issue if/when the population of the country nears 10 million? I presume that when  the individual's _PPSN _is eventually recycled?


 
I don't know if it is or not, I assumed not as tax liablities are still held against the estate of the deceased. I wouldn't be too impressed if my child received someone elses tax bill soon after receiving their PPSN.

Still doesn't account for transient workers who may only stay for 6 months and whose death can never be registered.


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## ClubMan (17 May 2006)

There's surprisingly little technical information about _PPSNs _online as far as I can see. I actually had two _PPSNs _(_RSI _numbers) in my time - one from when I was underage and lied about my age to get a summer job and another from when I "officially" started working under my real details. Tut, tut - I know but I was young, reckless and skint and don't have any record of the original _RSI _number at this stage...


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## porterbray (17 May 2006)

Many Revenue systems are programmed to take 8 digits and a letter eventually, when it becomes necessary. I presume that this will create a lot of hassle for employers payroll systems. The PPS could be in use for many years after someones death if the estate has liabilities. Anyway, PPS numbers are actually issued by Dept of Social Welfare, not Revenue, so I would presume they have made contingencies for having more than 10 million numbers available


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## ajapale (18 May 2006)

Thanks for the interesing insights!

I have cranked up excel and have been able to recreate the "mod 23" checksum validation. In the case of women with two characters at the end the validation ignores the ninth character (nearly but not always a W).

Thanks again.

aj


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