HMRC Red Flag Checker

HMRC now receives a lot more third-party data than it used to, from digital platforms, overseas banks, the Land Registry and crypto exchanges. The areas most likely to attract attention are usually the ones where what you have declared does not match what HMRC can already see. This tool walks through the six biggest red flag areas in 2026 and tells you, based on your situation, which of them apply to you, what you should be declaring, and roughly what you may owe. It is a quick screening check, not a full tax return, but it will tell you whether you have something to put right and which TheTaxGuide tool to use for a precise calculation.

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Find out which areas of your finances HMRC is most likely to query, what you should be declaring, and roughly what you may owe.

1 Roughly what was your total declared income on your last UK tax return?

2 Did you receive more than £1,000 of side-hustle or platform income last tax year? (eBay, Etsy, Vinted, Airbnb, Uber, Fiverr and similar)

3 Have you bought, sold or swapped any cryptoassets in the last tax year?

4 Do you receive any rental income?

5 Are you a director or shareholder of your own UK company?

6 Do you have any income, bank accounts, investments or property outside the UK?

7 Have you ever received an HMRC nudge letter or compliance enquiry about any of these areas?

8 Anything else HMRC should know about your situation? (optional)

Your privacy is protected. We do not store personal information. Names, addresses and details you enter are automatically removed.

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This tool gives general guidance about HMRC compliance risks based on the information you provide. It is not regulated tax advice. For your specific circumstances, consult a qualified accountant or contact HMRC directly. Any figures produced are rough estimates only.

What this tool does

The Red Flag Checker gives you a quick read on where your tax affairs are most likely to stand out to HMRC, based on the kind of income, assets or activity you have had in the last few years. It points out what should have been on your tax return, what probably was not, and gives you a rough idea of the tax, interest and penalties that could be in play.

It is a screening tool, not a full calculation. Think of it as a triage step before you decide whether to file, amend a return, or make a disclosure.

Who it is for

It is aimed at people who are not sure whether they have a problem, or who have a nagging feeling that something was missed. That includes anyone who has sold things on eBay, Vinted, Etsy or Depop, hosts on Airbnb, drives for Uber or delivers for Deliveroo, rents out a property, holds crypto, has a foreign bank account or overseas income, has sold a second home or buy to let, or receives income through a limited company or side business alongside a PAYE job.

It is also useful if you have had a nudge letter from HMRC and want to understand what triggered it before you reply.

How it works

You answer a short set of questions about your income, assets and any activity from the last four tax years. The tool then flags which of the six main risk areas apply to you, explains in plain English what HMRC can already see from third parties, tells you what you should have declared, and gives a rough figure for what you may owe. At the end you get a summary you can save or print, plus a pointer to the specific TheTaxGuide calculator that will give you an exact number. Your answers are processed in your browser for the check and are not saved to your account or shared with HMRC.

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