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How PayslipIQ Checks Your Payslip - Methodology & Sources

Plain-English methodology behind the PayslipIQ AI payslip checker - tax-code logic, PAYE, National Insurance, pension, student loan, refund signals, and our official sources.

Written by Priya Desai, MAAT - Payroll Methodology Editor.

Reviewed by Sarah Whitfield, ACA - Lead Editor, UK Payroll & Tax.

Last reviewed: 6 May 2026.

1. How our payslip checks work

PayslipIQ reads the structured fields on a UK or Irish payslip - gross pay, tax code, National Insurance, pension, student loan, net pay and pay date - and compares them against the relevant tax-year rules published by HMRC (or, for Ireland, Revenue.ie). Where the figures look broadly consistent, we mark them green. Where they look unusual but explainable, we mark them amber and explain why. Where they look meaningfully out of line with the rules we know about, we mark them red and suggest who to speak to.

Our checks are based on the information shown on the payslip and the circumstances you tell us about (for example, whether you are on Plan 2 student loan, or whether you contribute to a salary-sacrifice pension). We cannot see information that is not on the slip, so the check is only as complete as the slip you upload.

The PayslipIQ report is a structured second opinion. It is not a tax return, it is not a P800 calculation, and it is not a legally binding statement. HMRC, Revenue.ie and your payroll team remain the authoritative sources on your individual position.

2. Figures we may check

Depending on what your payslip shows and what you tell us, we may check:

3. Tax code logic

UK tax codes carry meaning in both the prefix and the suffix. Below is the logic PayslipIQ uses to interpret the most common codes. None of this replaces a call to HMRC; it is the starting point for our second opinion.

Where we cannot read the code clearly from the payslip, we say so and we do not guess.

4. PAYE income tax logic

For employees in England, Wales and Northern Ireland, PayslipIQ estimates expected PAYE using the tax-year personal allowance (currently £12,570 for 2025/26 unless your code says otherwise), the basic-rate band up to £50,270, the higher-rate band up to £125,140, and the additional-rate band above £125,140.

For Scottish taxpayers (S prefix), we apply the Scottish bands and rates as published by the Scottish Government for the relevant tax year.

We compare the expected PAYE for your period and your year-to-date totals against the figures on your slip. Differences of a few pounds are common and usually reflect rounding; differences of meaningful size trigger an amber or red flag with an explanation.

We do not cover every edge case (marriage allowance transfers, blind person's allowance, multiple simultaneous PAYE employments where HMRC has split the allowance, and certain expat-status cases). Where we detect such a case, we say so and suggest contacting HMRC.

5. National Insurance logic

For the 2025/26 tax year, the standard employee NI primary threshold and upper earnings limit are applied as published by HMRC. The default Category A employee rate is applied unless the payslip shows a different category letter (B, C, F, H, I, J, L, M, S, V, X, Z), in which case we apply the rate appropriate to that category.

We compare expected NI against the NI figure on your payslip. We flag meaningful deviations and explain the most common causes (wrong category letter, salary sacrifice reducing NIable pay, a deferment certificate, or a director on the alternative cumulative method).

NI rules change more often than most people realise - sometimes mid-tax-year. If the rate published by HMRC changes between our last review and your check, the report will note that we are using the rate from our most recent review.

6. Pension deduction logic

For workplace pensions, we check the deduction against the pension scheme details you provide (qualifying earnings band vs total earnings, employee contribution percentage, salary sacrifice or net pay or relief at source).

For auto-enrolment schemes, the statutory minimum total contribution is currently 8% of qualifying earnings, of which at least 3% must come from the employer. We compare the deduction on your slip against the percentage you tell us and against the auto-enrolment minimum.

Salary sacrifice schemes change both the gross pay and the NI calculation. Where you tell us a scheme is salary sacrifice, we adjust our PAYE and NI checks accordingly.

We do not give pension investment advice, we do not advise on consolidation, and we do not assess the suitability of any scheme.

7. Student loan and postgraduate loan logic

We support the four UK student loan plans (Plan 1, Plan 2, Plan 4 - Scotland, Plan 5 - for new students from 2023/24) and the Postgraduate Loan. We use the annualised income threshold for the plan you tell us about, divide it down to the relevant pay period, and check whether a deduction would be expected and roughly how much.

If your payslip shows a deduction but you have told us you are on no plan, we flag it red and suggest checking with payroll and the Student Loans Company. If your payslip shows no deduction but you are above the threshold for your stated plan, we also flag it.

8. Refund signals - explicitly cautious

PayslipIQ does not promise that you are owed a refund. Only HMRC can confirm that. What we can do is point out patterns on your payslip that often coincide with overpayment.

Examples of refund signals we may flag:

A refund signal is a question, not an answer. The right next step is to check your tax-year position directly with HMRC at gov.uk, which is free.

9. Why results are estimates

PayslipIQ produces estimates, not determinations. The reasons are simple, and we want to be upfront about them.

When a check is uncertain, we say so. When a check depends on something we cannot see, we ask you. When a check needs HMRC, we tell you.

10. Sources and updates

We rely on the following official sources, listed with the URL we treat as authoritative:

Last reviewed: 3 May 2026

Next review: by 3 November 2026, or sooner if HMRC, Revenue.ie, the Scottish Government, The Pensions Regulator, or the Student Loans Company publish a material change.

Corrections policy: /trust-centre#corrections - email editorial@payslipiq.co.uk to report a factual issue.

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