Thinking of building an app that checks your payslip for mistakes - would this be useful?

[k282001]

A lot of people I know (including me) have had payslips that were wrong without realising – overtime rate slightly off, wrong tax code, missing hours, holiday pay paid at basic rate instead of average, etc.

I was thinking of making a simple app where you upload your payslip (PDF or photo) and it checks for:
– wrong overtime rate
– incorrect tax code
– NI issues
– pension % wrong
– missing hours
– holiday pay miscalculated

Basically a quick “is this payslip right?” checker that flags possible mistakes.

If this existed, would anyone actually use it?

And would people be willing to pay a small subscription for monthly checks, or would this only be useful as a free tool?

Honest thoughts appreciated – trying to see if it’s worth building or if people would think “nah, I can read it myself”.

How would an app know that things were wrong?

Good question — it wouldn’t magically “know” everything, but it can flag things that don’t add up.

Example:
– You enter your hourly rate + overtime rate
– The app extracts the numbers from your payslip
– If the hours × rate don’t match the total, it flags it
– Same with tax code mismatches, NI brackets, pension %, etc.

It’s basically a calculator that says “this line doesn’t match what it should be” rather than pretending to know your entire payroll system.

Super simple, private, and all done on your device.

Out of curiosity — is this something you personally would pay a small monthly fee for, or would you only use it if it were free?

I wouldn’t put that sort of info into an unofficial app.

How safe would the information be kept?

Not for me.

Most work places have a HR rep of some kind to support with questions, if not a direct payroll team.

There are lots of other resources too such as HMRC and ACAS.

There is no way the app would know the correct tax code, only HMRC can help you with that.

Having worked in HR a long time, I do think we should include this in the curriculum. I have had some concerning questions about payslips over the years. Some
people don’t even look at them which blows my mind.

Just to clear things up — the app isn’t trying to replace HR, payroll, HMRC or anything like that.
It’s basically a simple checker that runs entirely on your phone and never sends payslip info anywhere.

A lot of people don’t know how to read their payslips, and mistakes do happen more than people think.
The idea is:

• You scan your payslip
• The app extracts the numbers locally (nothing uploaded or stored)
• It checks basic things like:
• • Do hours × rate match the total?
• • Is overtime calculated correctly?
• • Has the pension % changed?
• • Do deductions stay consistent month-to-month?
• • Are there obvious NI or tax mismatches compared to what it should roughly be?

It’s not pretending to know your company’s whole payroll system — it’s just a calculator that flags when something looks off so you can ask HR or HMRC if needed.

Privacy-wise:
– No accounts
– No cloud storage
– No sending payslips to a server
– Everything stays on the device, just like a normal camera or document-scanner app.

So it’s basically a quick “sanity check” for people who don’t know what they’re looking at, rather than anything official or risky.

Out of curiosity — if something like this existed and kept everything 100% offline, would you personally use it? Or would you only try it if it were completely free?

Totally fair point — that’s why the app wouldn’t store or send anything anywhere.
Nothing goes to a server, nothing is uploaded, nothing is saved.

It works the same way your phone’s calculator or camera works:
the scan is processed locally on the device and then deleted instantly.

So technically you’re not ‘putting info into an app’ — you’re just letting your phone read the numbers on the payslip and check the maths. No data leaves your phone at any point.”**

Totally get the concerns — that’s why the whole idea is for everything to stay 100% on your device.
No accounts, no cloud storage, no uploads, no servers. The app just reads the numbers on your payslip locally, checks the maths, and then deletes the scan unless you choose to save it.

So technically nothing is ever ‘sent’ anywhere — it never leaves your phone.

If it was kept completely offline like that, and purely helped you spot mistakes,
would you personally consider something like this for a small fee (e.g., £2.99/month),
or would you only use it if it were totally free?

I might try it but I wouldn't pay a subscription. Even if it worked well, I couldn't get over the resentment of paying a fee because I didn't trust someone else to do their job properly.

On the other hand, if you got this working well and integrated it into an existing HR or payroll system, a company might see that as an added value feature of that system, because it could save them admin time. Not sure it would make you any money that way though.

Far too much would go wrong. It’s just not a feasible idea.
And have you ever heard of an app which doesn’t store data? How would you monitor its effectiveness or fix mistakes, if you don’t store the data and review errors.

It sounds like a bit of a damp squib.

how would a user (this being someone who can’t do the maths themself) know for sure that an app which claimed it wasn’t uploading their data anywhere was telling the truth?

I’m sure you’re honest Op but there are too many fraudsters out there.

No, I can check all that myself. I understand my payslip just fine.

Would I work for Scottish tax codes? People with more than one job or a second self-employed income?

Money saving expert tax calculator is very good, I use that if I need to check anything.

Why have you used ChatGPT to write this post?

The problem would be that these people don't know their hourly rate. And if they tried to work it out they would almost certainly do it wrong.

For us, errors in overtime happen way before the payslip stage. The payslip will show x hours at x rate and that will be perfect. It is the number of hours coming out of the timesheet system that are more likely to be an issue.

There are free calculators online that will do this for you, I'm sure anyone who wanted to check could find one of those easily enough.

This. It’s not giving genuine Mumsnet user sense checking an idea.

An existing payroll system would already have this built in though, otherwise how would it produce the payslip in the first place.

My payslip doesn’t have my hours on it, so not sure what would be being checked tbh. Lots of people don’t really know what % they pay in pension contribution, nor whether it’s salary sacrificed or not - so I suspect your app would be telling people they’re not paying enough NI or tax.

What advantage would your app have over the existing websites where you can put in your salary, pension %, outstanding student loans etc and see what you should take home?

I don't understand what's it giving you that you can't already work out.

Also it's relying on users to give accurate data - if they knew that info, surely they wouldn't need to check it via an app?
You'd have to tell it e.g. your tax code, so surely you could check that yourself 😳

Lots of deductions change from month to month.

Do you have experience in building and developing apps?

Also if it's not storing data then how's it making any money, other than a low monthly subscription fee?

No, I know how to calculate this and there are several calculators online you can put your numbers in and it fits similar things. I agree with a PP that I think it’s madness never to check your payslip. My colleague doesn’t even know how much she earns…,

Thing is, everyone's payroll software will always be mathematically correct and apply the tax rules for the bit of the UK that apply. Your app would have no way of knowing whether you were due any overtime etc

Now this is an idea that might work. A "why does your payslip look like this" app within a payroll system.

ChatGPT detector says that is 0% AI and is 100% human written.

I don't see how you can check off just a payslip. For example:
How do you know from a payslip whether overtime should be time-and-a-half or double time? You'd need to see the contract.
How on earth are you going to check if their tax code is incorrect
How do you check NI if you don't know their DoB? (that's not on the payslip)
Etc etc.

There's no way I'd give an app access to my full name, address and NI number, regardless of any assurances. There are simple calculators online where you can enter figures only.

It's only going to appeal to people who can't do simple maths (eg your overtime example), so quite niche.

I can't see this being a goer myself.