Last Reviewed: March 2022

Paying your tax is supposed to be simple. For most people, it’s handled automatically through the Pay As You Earn (PAYE) scheme. For others, many of them self-employed, the Self Assessment tax return system is how they report their earnings and expenses. Either way, HMRC crunches the numbers and works out how much tax you owe. After that, the money’s either taken from your pay before you get it or you settle up yourself.

The trouble is, the taxman’s calculations are only as reliable as the information he’s working with. There are times where HMRC won’t have a complete and accurate picture of your work and financial situation When that happens, it’s easy to end up paying the wrong amount of tax without realising it – often for years at a time! Millions of pounds in overpaid tax goes unclaimed every year, and trying to claim it back isn’t always an easy process.

Here’s a quick run-down of the main reasons UK taxpayers find themselves owed a tax refund, along with some pointers on what to do about it.