HMRC sends a P800 letter when their end-of-year calculation shows you overpaid or underpaid tax through PAYE. Overpayments are automatically refunded (usually within 5 weeks); underpayments are collected via an adjustment to the following year's tax code.
Common reasons for overpaying: wrong tax code (e.g. BR used instead of 1257L), leaving a job mid-year without using the full Personal Allowance, or Marriage Allowance not being applied.
Result
—
Recommended tools
TC
Tax Claims UK — PAYE Tax Rebates
Specialists in PAYE tax refund claims. No refund, no fee.
Check my refund →
UB
Unbiased — Tax Adviser
Find a regulated tax adviser to maximise your refund claim.