HMRC is set to manually review 107,000 tax calculations from 2025/26 due to a longstanding computer-system flaw which incorrectly allocates taxpayers’ income and savings allowances. The problem, first identified in 2021, means HMRC’s systems do not always apply the "beneficial ordering" rules that should minimise a taxpayer’s bill. HMRC has not yet determined how many calculations are actually wrong, and experts warn that errors could remain undetected in cases not selected for review unless taxpayers spot them themselves. Stefanie Tremain of Blick Rothenberg said: "We may not be talking about huge amounts but you don't know how much that money is worth to the person who is receiving it." An HMRC spokesman noted that the number of calculations requiring a manual check is expected to fall to around 20,000 next year.
