An error by HM Revenue and Customs (HMRC) has led to a £1,476 overpayment in taxes for a UK taxpayer, who was incorrectly informed that they had £3,847 in untaxed savings interest instead of the actual £94. This mistake has resulted in a £200 monthly cut in their pay and raises concerns that others with Individual Savings Accounts (ISAs) may be similarly affected. Financial services company Zopa has warned that 'hundreds' could be impacted by this tax overpayment issue. The HMRC relies on annual returns from banks and building societies to pre-fill tax accounts, which can lead to discrepancies if previous year's data is inaccurate. Robyn Lovatt, a financial advisor, emphasized the ambiguity in how tax calculations are made, stating that estimates are often based on outdated information. HMRC has urged anyone who believes their tax information is incorrect to report it promptly to avoid overpayment or underpayment of taxes. Further updates from HMRC are anticipated soon, including changes to Child Benefit payment schedules.