The Final Countdown: Last-Minute Self-Assessment Tips Before 31 January

If you're reading this and you haven't yet filed your 2024/25 Self-Assessment tax return, you're not alone - HMRC figures consistently show that a huge proportion of returns are submitted in the final 48 hours before the 31 January deadline. The good news is that there is still time to get this right without panicking. Here's what to focus on if you're down to the wire.

First, Work Out What You Actually Need

Before anything else, take stock of exactly what's outstanding. Do you have your income figures - employment, self-employment, rental, dividends, interest? Do you know what expenses or reliefs you want to claim? If you're missing one specific document, such as a dividend voucher or a P60, it's often faster to estimate the figure using bank statements or online portals than to wait for a physical copy to arrive, provided you're confident the estimate is close to accurate.

If you're self-employed and your bookkeeping isn't up to date, resist the temptation to guess broad totals. Even at this late stage, it's worth taking an hour to go through bank statements and invoices properly, because an inaccurate return can cause more problems later than a late one - HMRC can charge penalties for inaccuracies as well as for lateness, and unpicking a wrong return is far more time-consuming than getting it right first time.

Filing Something Is Better Than Filing Nothing

If you genuinely cannot gather every figure in time, it is far better to file a return using your best reasonable estimates than to miss the deadline altogether. You can amend a Self-Assessment return after submission - HMRC gives you until the following 31 January to make corrections - so an imperfect but timely return, followed by an amendment once you have exact figures, is a much better outcome than a late return with an automatic penalty attached.

What Happens If You Miss the Deadline

It's worth understanding exactly how the penalty system works, because the structure matters for how urgently you should act if you do end up filing late. Miss 31 January and you get an automatic £100 penalty, even if you owe no tax at all or are in fact due a refund. If your return is still outstanding three months later, daily penalties of £10 kick in, up to a maximum of £900. At six months late, a further penalty of 5% of the tax owed or £300, whichever is greater, is added - and the same again at twelve months. On top of all this, interest accrues on any unpaid tax from the day after the deadline, regardless of when you actually file.

If You Can't Pay in Full

A separate but related worry for a lot of people at this time of year is being able to file the return but not being able to pay what's owed straight away. Filing on time and paying late are treated differently by HMRC, and it's important not to conflate them - always prioritise getting the return filed by the deadline even if you're still working out how to pay. If you can't pay in full, HMRC's online Time to Pay service allows many taxpayers to set up an instalment plan for self-assessment debts under £30,000 without needing to speak to anyone directly, which can be arranged in a matter of minutes and avoids the more serious penalties associated with simply not paying at all.

Don't Forget Payments on Account

If your tax bill for 2024/25 is significant and you didn't reduce your payments on account earlier in the year, remember that the amount due on 31 January typically includes not just your balancing payment for last year, but also the first payment on account for 2025/26. This can catch people out because the total due is often noticeably higher than the tax shown as owed for the year just gone. If your income has dropped since last year, it may be worth reviewing whether you can legitimately reduce your payments on account rather than overpaying and reclaiming later.

A Reasonable Excuse Is a High Bar

If circumstances genuinely prevent you from filing on time - a serious illness, a bereavement, a system failure at HMRC's end - you can appeal a late filing penalty on the grounds of a reasonable excuse. HMRC sets a high bar for what counts, and "I was too busy" or "I forgot" won't succeed, so this route should be seen as a genuine safety net rather than a plan.

Next Year, Start Earlier

Once this year's return is filed, it's worth taking five minutes to note down what made this year stressful, whether that was missing paperwork, unreconciled books, or simply not starting until the deadline was looming. A small change now - starting your return in the fourth quarter rather than the last week of January - makes an enormous difference to how this time of year feels going forward. If you'd like help making next year less of a scramble, we're always happy to talk about getting your affairs in order earlier.