The tax authority’s own guidance states that the taxable amount of state pension is calculated using one week at the previous year’s lower rate and 51 weeks at the current year’s rate to account for a small window between the start of the new tax year and the following Monday, when the new state pension rate kicks in.
But for more than 15 years, HMRC had instead been charging some pensioners for 52 weeks at the higher rate, using information provided by the Department for Work and Pensions.
Despite working on a fix since last autumn, Mr Marks confirmed that the error was yet to be resolved for pensioners in self-assessment. This means that figures that HMRC pre-populated in tax returns for 2025-26 as part of its automation drive remain too high for some pensioners.
The tax authority said that it had resolved the error going forward for retirees who have tax deducted automatically from their pension.
However, refunds for the last six tax years are not expected to be completed until March 2027 at the earliest.
For each year they were overtaxed, pensioners will on average be owed a rebate of £1.76 if they receive the full basic state pension and £2.30 if they receive the full new state pension.
However, wealthier retirees could be owed more. For example, an additional-rate taxpayer on the new state pension could receive up to £8.42 back for the 2023-24 tax year.
Refunds will be issued through tax code adjustments and credits to self-assessment accounts, or by cheque if necessary.
