The 31 January deadline lands in the worst week of the year for paperwork. Most people intend to sort their return in the autumn, then December arrives, and suddenly it is the second week of January and you are searching for a P60 you were sure you had put somewhere sensible.
The return itself is rarely the difficult part. Finding the numbers is. Gather the records first — before you open the software, before you dig out your Government Gateway password — and the job usually shrinks from three evenings to one. Below is a checklist of the twelve items that cover most returns, plus notes on the ones people forget.
Your Unique Taxpayer Reference is the ten-digit number HMRC sends when you register for Self Assessment. It appears on your notice to file, on previous returns and on most letters from HMRC. Without it, you cannot file. You will also need your National Insurance number and your Government Gateway user ID and password.
If you have not filed before, or your circumstances changed during the tax year, check whether you actually need to register. HMRC expects you to tell them by 5 October after the end of the tax year. Leaving registration until January is one of the most common reasons people miss the deadline, and late filing penalties start at £100.
Employers and pension providers report pay and tax through Real Time Information, so HMRC usually has your employment income before you do. Usually is not the same as always. Check the pre-populated figures against your own records, because a correction is far easier to make now than in a letter six months down the line.
Gather together:
If you sold shares, funds, crypto or property during the year, you will also need contract notes and transaction dates.
Reliefs are where money is quietly left on the table. If you pay into a personal pension from your bank account, the provider adds basic-rate relief and you claim the rest through your return, so you need a statement showing what you paid in.
Gift Aid works in a similar way, and plenty of people forget it entirely. Dig out bank statements or a charity's annual summary. Other items worth checking:
Nobody else is keeping these records for you, so keep them simple: a list of invoices raised, a list of expenses paid, and the receipts behind every number.
You will need rent received, letting agent statements, repairs, insurance, service charges and ground rent. Keep mortgage interest separate — for residential lets it is now given as a tax reducer rather than an allowable expense, so mixing it in with repairs will distort your figures.
A few things trip people up every January. Interest on a joint account is normally treated as split equally, so agree the split and note it down. Dividends that were reinvested are still dividends and still count. Old workplace pensions from a former job are easy to overlook, as are accounts closed partway through the year.
If you sold an asset you had held for years, the original cost figure can be buried in a broker statement from a decade ago. Start looking for that early, not on the 30th.
Estimating a figure is sometimes unavoidable. If you do, keep a note of how you arrived at it, so the number still makes sense to you if HMRC asks later. Once the return is filed, keep the paperwork. HMRC can check a return afterwards, and the general rule is to retain supporting records for at least five years after the 31 January deadline.
Filing early does not mean paying early. You can submit in October and still settle the bill by 31 January, which gives you time to budget rather than finding the whole amount in one month. If you make payments on account, the second instalment falls due by 31 July.
If you cannot pay in full, contact HMRC before the deadline to discuss a payment plan rather than ignoring the problem. Interest and penalties build quickly, and the £100 late filing penalty applies even if you owe nothing at all.
Know your limits, too. Dividends, property, foreign income,
