HMRC admits error: millions of pensioners overcharged in £43.5 million tax blunder
HM Revenue and Customs (HMRC) has admitted that up to 8.7 million pensioners have been overcharged on their income tax bills due to a software miscalculation that went undetected for nearly a year. The error, which inflated the reported value of the state pension for the 2025/26 tax year, is believed to have resulted in the taxman collecting approximately £43.5 million more than it should have.
HMRC has apologised for the mistake and stated that it is working to implement a fix later this summer. However, the department has not yet outlined a process for automatic refunds, leaving the onus on affected pensioners to identify the error and reclaim the money. The news has sparked sharp criticism from political figures, who have called for greater transparency and faster corrective action.
According to reports first published by The Sunday Times and subsequently confirmed by multiple outlets, including The Independent and the Daily Express, the flaw lies in how HMRC’s systems calculate state pension income for tax purposes. The state pension is paid gross, but remains subject to income tax. The error meant that millions of pensioners — those using self-assessment and those taxed through PAYE — saw their taxable income inflated by roughly £9.
The scale of the error
The headline figure of 8.7 million represents the total number of income-tax-paying pensioners who could have been affected. However, a narrower subset of 1.7 million pensioners who file annual self-assessment returns were directly impacted by a specific pre-filling error in HMRC’s online tool. For these individuals, the software automatically entered state pension income based on 52 weeks at the new, higher weekly rate. HMRC’s own published guidance states the correct figure should be one week at the old rate and 51 weeks at the new rate, reflecting the timing of the April uprating.
The discrepancy may appear small per person — approximately £5 extra in tax, on average, according to HMRC — but the cumulative effect is substantial. At the extremes, a higher-rate taxpayer could have been overcharged by £3.62, while an additional-rate payer would have seen an overcharge of £4. For basic-rate taxpayers, the typical overcharge was £1.81. HMRC’s own spokesperson acknowledged the error: “We apologise to those affected by this calculation error and are working to fix the issue, although the impact is small with the difference in tax owed being around £5 in most cases.”
How the error happened: the triple lock and a split-week gap
The root cause of the mistake lies in a discrepancy between how two government departments handle the same data. The Department for Work and Pensions (DWP) supplies state pension information to HMRC on a flat 52-week basis, using the new higher rate for all weeks of the year. HMRC’s own tax rules, however, require a split-week methodology. This is because the state pension is uprated in April each year under the triple lock — which guarantees an increase in line with the highest of average earnings, inflation, or 2.5% — but the start of the tax year (April 6) does not perfectly align with the first payment at the new rate.
For the 2025/26 tax year, the full new state pension rose from £221.20 per week to £230.25 per week. Under the split-week rule, only 51 weeks should be counted at the new rate, and one week at the old rate. HMRC’s pre-filled forms used 52 weeks at the new rate, inflating taxable state pension income by £9.05. That extra £9.05 triggered a small but widespread overcharge in income tax.
Accountancy firm Grant Thornton first identified the anomaly and brought it to public attention. The error affected both self-assessment filers and pensioners who remain in employment and pay tax via Pay As You Earn (PAYE). Because PAYE systems also rely on DWP data, the overcharge spread beyond the self-assessment pool.
Timeline: a delay in reporting
The timeline of events has drawn particular criticism. Conservative MP Richard Holden raised the issue in a parliamentary question in August 2025. According to The Sunday Times, HMRC did not alert the DWP about the problem until October — a gap of two months. The error was then allowed to persist for at least 10 months before a fix was publicly acknowledged. HMRC has said it has been working on a resolution since last year and expects to introduce a software patch “later this summer.”
Critics argue that the delay in informing the DWP and the public represents a failure of accountability. Shadow Chancellor Sir Mel Stride told The Times: “If HMRC have been charging millions of pensioners too much tax, then questions need to be answered, and the matter must be urgently put right. Ministers need to ascertain what has happened and what action is being taken to ensure these sorts of errors do not happen again.”
What this means for affected pensioners
For the millions of pensioners overcharged, the immediate question is whether they will receive automatic refunds. HMRC has not yet confirmed a system for proactively returning the money. Currently, the burden falls on the taxpayer to spot the error and make a claim. This is a significant concern for older taxpayers, many of whom may not have the digital literacy to navigate the self-assessment system or may not even be aware that an error has occurred.
Exchequer Secretary to the Treasury Dan Tomlinson, the minister responsible for HMRC, has stated that “most pensions do pay the right amount of tax in real time.” However, that reassurance does not extend to the millions caught in this specific miscalculation. Pensioners who filed a self-assessment return based on the pre-filled figure would have paid too much tax. Those on PAYE who had their tax code adjusted based on the inflated pension figure would also have been overcharged throughout the year.
Broader implications and trust in HMRC
This error is not an isolated incident. HMRC has faced repeated criticism in recent years for systemic failures in its computer systems, including the well-documented problems with the tax credit and child benefit systems, as well as the troubled rollout of the Making Tax Digital initiative. Each incident erodes public confidence in the tax authority’s ability to administer the system fairly and accurately.
The pensioner tax blunder also highlights a structural issue: the disconnect between DWP and HMRC data systems. While both are government departments, they operate on different reporting conventions, and those differences are not automatically reconciled. The result is that millions of pensioners — among the least likely demographic to challenge a tax calculation — are left to pay the price for an administrative mismatch.
In a broader sense, this case raises questions about the adequacy of HMRC’s testing and quality assurance processes. If an error of this magnitude — affecting up to 8.7 million people — can go unnoticed for nearly a year, it suggests that the organisation’s internal checks are insufficient. The fact that the fault was initially flagged by an opposition MP and then by an external accountancy firm, rather than by HMRC’s own compliance teams, is particularly troubling.
What happens next
HMRC has committed to deploying a fix later this summer, but has not provided a specific date. The department has also not clarified whether refunds will be issued automatically or whether affected pensioners will need to actively claim. For those who filed self-assessment, there is some precedent: HMRC can adjust tax codes for future years to recover overpayments, but this does not provide immediate reimbursement.
Pensioners who believe they may have been overcharged are advised to check their tax calculation for the 2025/26 tax year. Those who used self-assessment should verify that the state pension figure entered was based on 51 weeks at the new rate and one week at the old rate. Anyone who finds an error should contact HMRC directly to request a correction.
In the meantime, political pressure is mounting. Shadow Chancellor Sir Mel Stride has demanded a full accounting of how many pensioners were affected and a plan for refunds. The government has yet to issue a formal response beyond the HMRC apology.
Conclusion
The HMRC pensioner tax error is a story of a small administrative flaw with a very large human impact. While the average overcharge is only £5, the cumulative total of £43.5 million represents money that should never have been taken from pensioners in the first place. The fact that the error persisted for months, despite being flagged internally and externally, points to deeper systemic weaknesses within the tax authority. As summer approaches and the promised fix draws nearer, the focus will shift from apology to action — and from acknowledgment to refund.
For now, millions of older taxpayers are left wondering if they have been overcharged and, if so, how they will get their money back. The answer may determine whether this episode becomes a minor footnote or a lasting stain on HMRC’s reputation.
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