What to Do When HMRC Wants Tax Money Back: A Complete Guide

---

If HM Revenue and Customs (HMRC) contacts you to say you owe them tax money, the very first thing you need to do is check if their calculation is correct. Do not panic, but do not ignore the letter or bill either. Compare their figures against your own records (like your payslips, P60, or tax returns). If you agree that you owe the money but cannot afford to pay it in one go, contact HMRC straight away to set up a monthly payment plan called a “Time to Pay” arrangement.

---

Opening the post or checking your online account to find a demand for tax is a massive shock. Whether you are employed, self-employed, or being asked to pay for a mistake made years ago, it is easy to feel overwhelmed.

Here is a simple breakdown of why HMRC might want money back, and exactly what steps you should take for your specific situation.

1: You Are Employed (PAYE)

If you get your income from an employer or a pension provider, they handle your tax automatically. However, underpaying is common—especially if you changed jobs, had more than one income, or were on the wrong tax code.

HMRC usually sends one of two letters to employees:

• A P800 Tax Calculation: This is a standard end-of-year letter showing you paid too little tax. If the amount you owe is under £3,000, HMRC will usually just change your tax code for the next tax year. This means they will quietly take slightly more tax out of your monthly pay packet in 12 equal instalments. You do not need to find a lump sum.
• A Simple Assessment: You will get this if you owe £3,000 or more, or if the tax cannot be taken out of your regular wages. You cannot pay this through your tax code, so you will have to pay HMRC directly by the deadline on the letter.

What to do: Dig out your P60, P45, or P11D forms. Check the numbers on HMRC’s letter. If they are wrong, call them to get it corrected.

2: You Are Self-Employed (Self Assessment)

Running a business is hard enough without getting hit by a massive tax bill in January. If your Self Assessment calculation is much higher than you expected, it is usually because of one specific rule.

• The “Payments on Account” Shock: HMRC expects self-employed people to pay their tax in advance. Your January bill often includes the tax you owe for the year that just ended, plus an extra 50% advance payment towards next year’s estimated bill.
• How to fix it: If your income has dropped recently and you know you will not earn as much this year, you can log into your HMRC account and ask to “reduce your Payments on Account.” This will instantly shrink your bill.
• A golden rule: Even if you cannot afford the bill, file your tax return on time anyway. HMRC charges automatic £100 fines for missing the 31 January deadline. You cannot ask them for a payment plan until your return is officially submitted.

3: HMRC Wants Tax from a Past Year

Sometimes HMRC will ask for money regarding a tax year that ended a long time ago. This can happen to anyone, and usually comes in the form of a formal check.

• Compliance Checks or Discovery Assessments: HMRC can review your past tax affairs if they think tax was underpaid. This might be triggered by a simple mistake on an old form, or because they received new information (like data from a bank or an old employer). Depending on the circumstances, they can look back anywhere from 4 to 20 years.
• What to do: Do not assume they are right. Read the letter carefully and dig out your old bank statements, receipts, and returns. Did they miss something? Did they forget to include tax you already paid?
• How to appeal: If you disagree with their decision, you usually have 30 days to appeal in writing. Include copies (never originals) of any evidence that proves you paid the right amount.

What to Do If You Cannot Afford to Pay

No matter which scenario applies to you, if you agree that you owe the money but do not have the cash to pay it, do not ignore the problem. HMRC will add interest to the debt and eventually take debt collection action.

Instead, you need to set up a “Time to Pay” arrangement. This is a customised payment plan that lets you spread your tax bill over several months based on what you can genuinely afford.

• If you are self-employed: You can usually set this up online in five minutes without speaking to anyone, provided you owe £30,000 or less, plan to clear the debt within 12 months, and apply within 60 days of the payment deadline.
• If you are employed or owe more than £30,000: Call the HMRC payment helpline before your deadline. Work out your household budget before you dial so you know exactly how much you can afford to offer them each month. As long as you reach out early, HMRC is generally very willing to help you get back on track.

---