Can't File Your Tax Return by 31 January? What Happens and What to Do

If you can't file your Self Assessment return by 31 January, you get a £100 late filing penalty straight away — even if you owe no tax. The penalties then grow: £10 a day from 1 May for up to 90 days, then 5% of the tax due (or £300 if more) at six and twelve months. Interest runs on unpaid tax from 1 February. Paying an estimate on time and filing as soon as you can keeps the cost down.

The penalties for filing late

• 1 day late: £100 fixed penalty.

• 3 months late: £10 a day for up to 90 days — a further £900.

• 6 months late: 5% of the tax due or £300, whichever is greater.

• 12 months late: another 5% or £300, and more if HMRC decides information was withheld.

Paying late is a separate charge

Late payment is charged separately from late filing. Interest runs on unpaid tax from 1 February at HMRC's late payment rate, currently 7.75% a year, and late payment penalties of 5% of the unpaid tax are added at 30 days, six months and twelve months.

The two problems are independent: you can pay on time without having filed. If you know roughly what you owe, pay that amount by 31 January. It stops interest and late payment penalties on whatever you have paid, even while the return itself is late.

What to do if you can't file in time

• Pay an estimate of the tax by 31 January, using last year's figures as a guide.

• File as soon as you can — the daily penalties only start on 1 May.

• If you can't pay, set up a Time to Pay arrangement with HMRC before the deadline.

• If something outside your control stopped you, appeal the penalty with a reasonable excuse.

Reasonable excuse

HMRC cancels penalties where there was a reasonable excuse — serious illness, a bereavement close to the deadline, an HMRC system failure or a fire or flood, for example. Forgetting, being busy or relying on someone else to file usually isn't enough. Appeal within 30 days of the penalty notice, and file the return as soon as the excuse ends.

Payments on account still apply

If last year's bill was over £1,000, the January payment also includes the first payment on account for the current year. A late return doesn't change that — but if your income has fallen, you can ask HMRC to reduce the payments on account.

Use our HMRC interest and penalties calculator to see what a late return will cost, or our payments on account calculator to work out the January bill. If you'd like it taken off your hands, our Self Assessment service in Glasgow can prepare and file the return.