The IR35 offset rule — what it is, how it works, and when it might not apply
Direct Answer
The IR35 offset rule, introduced in April 2024, prevents double taxation when HMRC successfully challenges an outside IR35 determination. If HMRC wins a case and the fee-payer or client owes tax, any tax already paid by the contractor's limited company must be offset against that liability. This was a significant improvement — but the offset is not automatic, not guaranteed in every case, and recent developments show it will not always be applied. Understanding when it applies matters.
What problem does the offset rule solve?
Before April 2024: if HMRC challenged an outside IR35 determination and won, the fee-payer (agency or client) owed PAYE and NICs on the contractor's income — but the contractor had also already paid corporation tax and dividend tax through their limited company.
This created double taxation: the same income taxed twice. The offset rule requires HMRC to credit taxes already paid by the contractor's company against the fee-payer's liability.
How does it work in practice?
If HMRC wins an IR35 challenge against your end-client or agency, they must calculate what tax you (through your limited company) have already paid on that income. That amount is offset against the PAYE/NICs liability that the fee-payer owes. In theory this prevents the same money being taxed twice.
When might the offset NOT apply?
The offset is a legal mechanism — but applying it requires HMRC to actively calculate and credit the amounts. In complex cases involving multiple parties, long time periods, or large sums, the offset calculation is not straightforward.
Recent cases have shown that the offset mechanism does not always function as intended in practice — particularly in large-scale or public sector disputes. Contractors should not assume that an HMRC challenge automatically results in fair treatment of taxes already paid.
What does this mean for contractors operating outside IR35?
The offset rule is a protection — but not a guarantee. The best protection remains a properly assessed and documented outside IR35 status in the first place.
If HMRC challenges your status, your limited company's tax position matters — keep records of all taxes paid. Work with an accountant who understands IR35 compliance, not just annual filing.
IR35 compliance is not just about your contract — it's about your whole company structure.
Autobooks advises on this as standard.
Full-service contractor accountancy from £89+VAT/month.