P800 / Simple Assessment Decoder

A P800 says HMRC think you have underpaid or overpaid tax. A Simple Assessment is similar but for State Pension and other complications. PaySlipIQ explains what is going on and whether HMRC have got it right.

P800 vs Simple Assessment

P800 — issued when HMRC end-of-year reconciliation says you overpaid or underpaid tax via PAYE. If you overpaid, HMRC will refund you (cheque or direct payment to your tax account). If you underpaid, HMRC normally collects it via your tax code the following year.

Simple Assessment — used when HMRC can collect a small underpayment without forcing you onto self-assessment. You normally have 3 months to pay or appeal.

When is a P800 wrong?

• • HMRC missed a tax-deductible expense (uniform, professional fees, mileage)
• • Pension contribution relief at higher rate not applied
• • Marriage Allowance not factored in
• • Two employments with overlapping tax codes
• • Bank statements showing taxed interest treated as untaxed
• • Employer payroll figures differ from HMRC record (RTI mismatch)

How to dispute a P800

1. Do not ignore it. Time limits are tight (60 days for P800).
2. Check your HMRC personal tax account at gov.uk/personal-tax-account.
3. Phone HMRC on 0300 200 3300.
4. If HMRC will not budge, request a statutory review.
5. Free help is available from TaxAid (low-income workers) or Tax Help for Older People.

Disclaimer: Educational guidance only. Time limits on tax appeals are strict — for complex cases consult a qualified tax adviser, an accountant, or a free-of-charge charity such as TaxAid or Tax Help for Older People.