The 31 January deadline has passed. You did not file. You are now in a race — not against HMRC exactly, but against a penalty clock that starts ticking immediately and compounds every month you leave it.
The good news: there is a significant difference between acting today and acting in three months. Here are the three things to do, in the order that matters.
Thing 1: File the return now — even if it's not perfect
The most expensive mistake people make after missing the deadline is waiting until they have everything perfectly organised before filing. Meanwhile, the penalty clock runs.
HMRC allows you to file a Self Assessment return with estimated figures, noting that an amendment will follow once you have all your records. Filing on estimates — even rough ones — immediately stops any further daily penalty charges from accumulating (once the three-month threshold hits), prevents HMRC from issuing a determination, and opens the door for penalty appeals to be processed.
Perfect is the enemy of done when HMRC penalties are compounding. File something. Fix it later.
Thing 2: Check your appeal window before it closes
Once your return is filed, you have a 30-day window from the date on the penalty notice to formally appeal the £100 fine — and any subsequent fines — on reasonable excuse grounds. This window is fixed. Miss it and your options narrow significantly.
Look at the date on the penalty letter. Count 30 days forward. If you are still inside that window, an appeal may be worth pursuing. The grounds that HMRC accepts include serious illness (yours or a close relative's), bereavement, unexpected hospital admission, HMRC's own system failures, fire, flood, or theft. The grounds that do not work include being busy, not knowing the deadline existed, or finding the return too complicated.
Even if you do not have an obvious excuse, do not assume an appeal is impossible. A specialist who handles these cases regularly will know the framing that gives you the best chance.
Thing 3: Sort the underlying tax payment — or arrange a plan
Filing the return stops the filing penalties from escalating. But if you owe tax and cannot pay it, that is a separate problem with separate consequences. HMRC charges interest on unpaid tax from 31 January, compounding daily. Ignoring the payment side while dealing with the filing side means interest accumulates throughout.
If you cannot pay in full, HMRC has a Time to Pay arrangement — a formal monthly payment plan that stops enforcement action. For debts under £30,000 you can apply online. For larger amounts, you will need to negotiate directly, which is where a specialist who knows how to present a financial case to HMRC's debt management team makes a material difference to the terms you get.
Why the order matters
File first. Appeal second. Sort the payment third. That sequence matters because HMRC will not process a penalty appeal on an outstanding return. And a payment plan is easier to negotiate when the return is already filed and HMRC can see the actual liability.
The alternative — waiting until you have the time, the records, and the money all organised simultaneously — is rarely how it plays out. Something will slip, the three-month daily penalty threshold will pass, and a manageable problem becomes a much larger one.
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