HMRC forced to check 100,000 tax bills after five-year computer glitch leaves Brits out of pocket

HMRC will be forced to review 100,000 tax bills after a computer glitch left Brits out of pocket. Taxpayers began flagging mistakes back in 2021, with the tax office admitting there were errors with calculating people’s tax. These issues are believed to be as a result of flaws in the HMRC computer system, which has yet to be fixed. It means that the tax authority has to manually check thousands of tax calculations every year to make sure they are right. Sign up for the Money newsletter Thank you! Some taxpayers have been left overpaying tax due to the blunders, as they didn’t get all the tax allowances they were entitled to. Some 107,000 tax calculations from the 2025-26 tax year that HMRC suspects could be wrong will have to be checked, according to The Telegraph. The errors are related to the calculation of “beneficial ordering” – a rule that requires HMRC to calculate taxpayer’s personal allowances and tax bands in a way that results in the lowest possible total tax bill. Everyone in the UK is entitled to earn £12,570 before they start paying tax – known as your personal allowance. Aside from this, there are a number of other allowances, including marriage allowance for couples, a trading allowance of £1,000 for people with side hustles, and a personal savings allowance of up to £1,000 of savings interest tax-free. HMRC said it expects the number of cases needing to be manually reviewed to drop next year. Most read in Money A HMRC spokesman told The Telegraph: “We take extensive action to identify the minority of customers who may be affected and update their tax calculations as needed to ensure they pay the right tax. “The number of calculations requiring a manual check is expected to fall to around 20,000 next year.” Comment now