The nine most common reasons your UK payslip does not add up — and exactly what to check next, in plain English.
Likely causes: Wrong tax code (e.g. emergency BR / 0T), unclaimed Marriage Allowance, student loan now triggered, pension auto-enrolment kicking in.
What to do: Compare your tax code on this payslip with last month P60. If different, check our Tax Code Checker.
Decode your tax code →Likely causes: Tax code on a non-cumulative basis (W1 / M1), bonus pushed you into the 40% band for one period, employer using emergency code while waiting for HMRC.
What to do: Check whether the code on the payslip ends in W1, M1 or X. If yes, it is non-cumulative and may correct itself or trigger a refund at year end.
Check your full payslip →Likely causes: Cut-off date for the period, payroll lag (paid next month), wrong shift logged, hours not approved by manager.
What to do: Check the period dates on the payslip. Overtime worked AFTER the period end is usually paid the following month.
How payslip periods work →Likely causes: Auto-enrolment opt-in raised contribution to 5%, salary sacrifice scheme started, employer increased default rate.
What to do: Check the pension percentage shown on payslip vs your scheme rate. Most UK auto-enrolment is 5% employee + 3% employer minimum.
Pension calculator →Likely causes: Earnings crossed the £12,570 Primary Threshold, NI category letter changed (apprentice / married woman / state pensioner), 8% main rate now applies.
What to do: Check the NI category letter on the payslip. Most employees are Category A (8% / 2%).
NI calculator →Likely causes: No P45 from previous employer means your new employer uses an emergency tax code (1257L W1), starter checklist Statement A/B/C affects rate.
What to do: Submit your P45 or starter checklist as soon as possible. HMRC usually corrects the code within 1 to 2 pay cycles.
P45 explained →Likely causes: Earnings now exceed Plan threshold (Plan 1 £26,900, Plan 2 £29,385, Plan 4 £33,795, Plan 5 £25,000, Postgraduate £21,000).
What to do: Verify which plan applies — your loan agreement letter shows it. Wrong plan equals wrong deduction.
Student loan calculator →Likely causes: HMRC issued a coding adjustment, you paid emergency tax that has now been corrected, P800 calculation was reconciled.
What to do: A negative tax figure means HMRC has refunded you through payroll. Confirm the new tax code is correct.
P800 explained →Likely causes: Attachment of Earnings Order (AEO) for unpaid debts, child maintenance, council tax arrears, or court fines.
What to do: Your employer is legally required to deduct this. Contact the issuing authority to confirm the amount and resolve the underlying debt.
Read full glossary →Upload your payslip. PayslipIQ checks every figure against UK 2026/27 payroll rules and flags anything unusual — in under 30 seconds. Files are deleted automatically after analysis.
Check my payslip now →