Brits could be owed hundreds of pounds from HM Revenue & Customs (HMRC), but it is their responsibility to check. Speaking on his BBC Sounds and Apple Music podcast, the MoneySavingExpert.com founder said: "The scale of the problem is significant."
5.6 million people overpaid a combined £3.5 billion in income tax in the most recent tax year, with the average overpayment standing at around £689, according to a Freedom of Information request submitted by accountancy firm UHY Hacker Young.
Martin added: "Millions of codes are wrong each year, so it's crucial to check yours — it's your responsibility, not your employer's, not HMRC's."
"Do not assume that because it's coming from HMRC that it is right. Millions — and that is not an exaggeration, it's a literal fact — millions are wrong every year," the finance guru previously said.
HMRC paid around £3 billion back to 4.2 million people who had overpaid in the 2024/25 tax year alone, according to MoneySavingExpert's own FOI data — but crucially, HMRC is under no legal obligation to notify individuals of overpayments or issue refunds automatically.
A tax code is the series of numbers and letters on a payslip that tells an employer or pension provider how much income tax to deduct. The most common code for the 2026/27 tax year is 1257L, which reflects the standard £12,570 personal allowance. If yours looks different and you are unsure why, it is worth checking.
Errors are most likely to creep in after a life change. Lewis has flagged the most common triggers — starting a new job without a P45, having workplace benefits such as a company car end, receiving multiple sources of income, or starting to draw a pension. In any of these situations, HMRC may be working from out of date information.
The good news is that overpaid tax can be reclaimed. HMRC allows claims to be backdated for up to four years, meaning anyone who suspects they have been on the wrong code can potentially recover a significant sum.
