Cumulative tax calculation
UK tax glossary · Last reviewed: April 2026
A cumulative code looks at everything you have earned and tax paid since 6 April. Each payslip adjusts for earlier periods, smoothing allowances across the year.
Non-cumulative W1/M1 codes ignore earlier pay — a common cause of emergency overpayment.
TaxHelper provides general information based on published HMRC rates and guidance. It is not regulated financial or tax advice. For decisions involving significant sums, complex circumstances, or if you are unsure, speak to a qualified accountant or HMRC directly.