How far back can HMRC go on IR35?

There is no dedicated IR35 time limit written into the legislation. HMRC uses the standard assessment time limits that apply across income tax, National Insurance, and corporation tax.

How far back HMRC can go depends on why the status position was wrong, not on the fact that it involves IR35 specifically. A genuine, reasonable mistake reaches back less far than a careless or deliberate one.

In practice, HMRC has opened IR35 reviews covering several tax years at once, particularly where a business used the same contracting model across its whole contractor population.

IR35 and off-payroll working status are decided under Chapter 8 Part 2 ITEPA 2003 (opens in a new tab) and Chapter 10 Part 2 ITEPA 2003, but the assessment time limits come from general tax administration law, not from these chapters themselves.

Where a business or personal service company took reasonable care but still got the status decision wrong, HMRC's assessment window is shorter than where it did not.

Where the error is careless, the window extends to a longer period; where HMRC concludes the failure to apply the right status was deliberate, the window extends further still, using the discovery powers in Schedule 18 Finance Act 1998 alongside the Taxes Management Act 1970 for personal liabilities.

Because off-payroll status reviews often span multiple contractors and multiple years, the practical effect of a wide review can feel larger than a single-year enquiry, even though each year is still assessed against its own time limit.

Keep status determination statements, contracts, and working practice evidence for at least as long as the longest possible assessment window, not just the standard record-keeping period.

If HMRC opens a review covering several years, check each year's position individually; the behaviour finding, and therefore the time limit, can differ year to year depending on what evidence existed at the time.

Where a client's status determination changed over time, keep a record of when and why, since that history affects how HMRC characterises earlier years.

A multi-year IR35 review can mean several years of backdated PAYE, National Insurance, and interest, which adds up quickly compared with a single-year dispute.

Penalties depend on the behaviour finding for each year, so a strong case for reasonable care in earlier years can materially reduce the overall exposure.

Reviewing several years of contracts and working evidence takes real time and specialist judgement. Growth plan clients get free tax investigation insurance included, covering the professional costs of defending an enquiry like this — see /fees.

Do not assume a single, blanket time limit applies across every year under review; each year is assessed on its own facts.

Do not discard old contracts or status paperwork once the standard filing retention period passes; HMRC's assessment window can be longer.

Do not accept HMRC's characterisation of behaviour without challenge; the difference between careless and deliberate materially changes both the time limit and the penalty.