If you have sold a property, investment, or business asset and are wondering what your capital gains tax exposure might be, obtaining an answer to the question ‘How far back can HMRC go for capital gains tax?’ is crucial.
For a confidential free discussion, call us today on 01908 538294, alternatively email us at Hello@altion-law.co.uk or complete our Free Enquiry Form and we will call you back.
The starting point
For most taxpayers who have made a genuine mistake or omitted a gain without any intent to deceive, HMRC’s standard time limit for raising an assessment is four years from the end of the tax year in which the liability arose.
When carelessness extends the window to six years
Where HMRC forms the view that a taxpayer has been careless, the time limit extends to six years. Carelessness in this context does not necessarily mean dishonesty. It can include failing to take reasonable care when completing a return, misunderstanding whether a gain was reportable, or relying on incorrect advice without properly questioning it. The distinction between an innocent mistake and a careless one is not always obvious, and it is frequently contested.
If you are facing an HMRC enquiry or have reason to believe your past returns may have been inaccurate, our HMRC solicitors can assess your position and advise you on the applicable time limit and your likely exposure before the situation escalates.
Offshore assets
A significant extension applies where capital gains arise from offshore sources. Where a taxpayer has failed to disclose gains connected to offshore assets, accounts, or structures, HMRC can go back 12 years, even where the failure was not deliberate. This rule was introduced to give HMRC additional time to investigate the more complex and often opaque arrangements that offshore income and gains can involve.
With the increasing flow of international financial information to HMRC through automatic exchange agreements such as the Common Reporting Standard, offshore arrangements that were once difficult to detect are now far more visible to the authorities. We advise clients on their offshore disclosure obligations regularly, and early, voluntary disclosure almost always produces a better outcome than waiting for HMRC to make contact.
The 20-year rule: deliberate behaviour
The furthest HMRC can go back for capital gains tax is 20 years. This time limit applies where HMRC takes the view that the loss of tax was brought about by deliberate conduct, such as knowingly filing an inaccurate return, actively concealing a gain, or adopting a position the taxpayer knew to be wrong. It also applies where a taxpayer has failed to notify HMRC of a liability without a reasonable excuse, regardless of whether there was any active dishonesty involved.
Discovery assessments
HMRC has the power to issue a discovery assessment when it identifies information that was not previously before it. This allows HMRC to open up older years even after the standard enquiry window has passed, provided it can demonstrate it has genuinely discovered something new.
Critically, HMRC can also change its position as an investigation progresses. An enquiry that begins under the four-year rule can be escalated to the six-year or even 20-year window if HMRC uncovers evidence of carelessness or deliberate conduct during the process. This is one reason why managing an HMRC investigation carefully from the outset is so important, and why having specialist legal representation early can make a material difference to the outcome.
CGT reporting obligations and deadlines
For residential property disposals, HMRC requires taxpayers to report and pay capital gains tax within 60 days of completion. Missing this deadline attracts automatic penalties, and a late return will itself flag the transaction for a compliance check. For other assets reported through self-assessment, the annual return deadline applies.
Failing to file at all does not protect a taxpayer from liability. It simply removes the protection of the shorter time limits and can push the analysis toward the 20-year window.
At Altion Law, we assist clients with CGT compliance, including late reporting, voluntary disclosure, and penalty mitigation, making sure that where something has gone wrong, it is addressed in the most favourable way available.
What to do if you have concerns
If you have sold an asset, received a capital distribution, or inherited property that was later disposed of, and are uncertain whether the correct gain was reported, taking early advice is the single most important step. While HMRC’s Digital Disclosure Service is available, using it effectively requires careful preparation to avoid inadvertently conceding more than is necessary.
Our tax team has extensive experience in HMRC investigations, voluntary disclosures, and tax tribunal proceedings. Whether you are facing an active enquiry or simply want to understand your exposure before HMRC makes contact, we provide clear, practical advice tailored to your circumstances. Contact us to arrange an initial discussion.
For a confidential free discussion, call us today on 01908 538294, alternatively email us at Hello@altion-law.co.uk or complete our Free Enquiry Form and we will call you back.
