How Far Back Can HMRC Go on Offshore Income? The 4, 6, 12 and 20-Year Rules

One of the first questions people ask about undeclared overseas income is simple: how far back can HMRC go?

For offshore income and gains, the answer is often further than you might expect. This guide explains the time limits clearly, with examples.

The normal UK time limits

For UK-only income, HMRC’s time limits for raising an assessment depend on why tax was underpaid:

The clock runs from the end of the tax year concerned, which is 5 April.

The 12-year rule for offshore matters

From 2019, the law changed for Income Tax, Capital Gains Tax and Inheritance Tax involving offshore matters.

Where tax is lost because of overseas income, assets or transfers, HMRC can usually assess up to 12 years after the end of the tax year, even if the error was innocent or careless.

The 12-year limit does not apply in some cases where HMRC already received the information from abroad, for example under automatic exchange, in time to act within the normal limit.

Which years are still open in 2026?

As at November 2026, the earliest tax years HMRC can usually still assess for offshore matters are:

Each year that passes closes another tax year. But waiting is not a strategy. Penalties are lower for unprompted disclosures, and HMRC’s data on overseas accounts keeps growing.

Why your behaviour category matters so much

The behaviour category affects two things at once:

1. How many years the disclosure must cover.
2. The penalty percentage charged on the tax for each year.

For example, a careless error might mean 12 years of offshore income with a modest penalty. A deliberate one could mean 20 years with a far higher penalty.

So the reasoning must be honest, clear and supported by evidence. Our guide to WDF penalties explains the ranges.

What counts as careless or deliberate?

• Reasonable care: you took proper steps, such as following professional advice, but still made an error.
• Careless: you did not take enough care, for example not checking whether foreign interest was taxable.
• Deliberate: you knew the income should be declared and chose not to.

Most people with forgotten savings or rent abroad fall into the careless category. Each case still depends on its own facts.

Does Inheritance Tax have the same rule?

Largely, yes. For Inheritance Tax involving offshore assets, a 12-year limit can also apply to transfers from 1 April 2015 where there was no careless or deliberate behaviour. Deliberate cases remain at 20 years.

This matters for executors dealing with estates that include overseas property or accounts. Personal representatives can use the Worldwide Disclosure Facility to put right a deceased person’s tax affairs.

What this means for your disclosure

• A WDF disclosure should cover every year still open for your behaviour category.
• You need records for each year, or reasonable estimates where records are lost.
• Interest runs on the tax for each year, so older years cost more in interest.

If records are missing, an accountant can help build reasonable, explained estimates that HMRC is likely to accept.

A quick example

Illustration only. Raj moved to the UK in 2012 and kept a rental flat abroad. He never reported the rent. He comes forward in 2026 and his error is accepted as careless.

• Under UK-only rules, HMRC could look back 6 years.
• Because the income is offshore, the disclosure must usually go back to 2014/15, which is 12 years.
• Each year includes tax, interest and a penalty based on careless behaviour.

Had HMRC found the flat first, the penalty would have been higher and Raj would have had less control over the timing.