HMRC has published a survey, carried out ahead of World Mental Health Day on 10 October, of more than 5,200 customers: over 26% said they feel anxious when a tax or financial deadline is approaching. Its response is to tell Self Assessment customers to start their 2025 to 2026 tax return now, more than three months before the 31 January 2027 payment and online filing deadline, rather than leaving it until January. HMRC's Chief Customer Officer, Myrtle Lloyd, put it plainly: "Self Assessment doesn't need to be overwhelming, by starting early you have time to prepare properly and complete your tax return in manageable bitesize chunks, which is always better." More than 24,000 people filed their return on World Mental Health Day itself last year.
What's actually changed for this tax year
Behind the headline tip, there are real mechanical differences worth knowing before you start. Paper returns for 2025 to 2026 are due by 31 October 2026 — a date that, for most people now filing online, has already quietly passed as a live option. The online filing and payment deadline is 31 January 2027. If you'd rather HMRC collect what you owe through next year's tax code instead of paying it as one amount, and the bill is under £3,000, you need to file online by 30 December 2026, which is a much tighter window than it sounds once November and the Christmas period are accounted for.
Two new pieces of pre-population also land on this year's return. Around 300,000 customers who pay the High Income Child Benefit Charge through Self Assessment will now find their own or their partner's Child Benefit payment details already filled in, rather than having to track the figures down themselves. And anyone who received the 2025 to 2026 Winter Fuel Payment, or the Pension Age Winter Heating Payment in Scotland, will see it pre-populated too — relevant because anyone with total income over £35,000 pays that payment back through their Self Assessment bill. Both are worth checking rather than assuming they're right, since a pre-filled figure is still your responsibility to confirm.
The arithmetic behind "a big bill all at once"
HMRC's own advice list includes budgeting for the bill "rather than facing a big bill all at once." That's easy to say and hard to picture, so here's what it actually looks like in cash terms for an illustrative sole trader with £45,000 of profit for 2025 to 2026, filing a Self Assessment return for the first time, with no payments on account already made towards this year. The figures below use the confirmed 2025-26 personal allowance of £12,570, the 20% basic rate of income tax, and the Class 4 National Insurance rate of 6% on profits between £12,570 and £50,270 — they are illustrative only, not any client's real figures.
Income tax is due on £32,430 of taxable profit (£45,000 minus the £12,570 personal allowance) at 20%, which comes to £6,486. Class 4 National Insurance is due on the same £32,430 at 6%, which comes to £1,946. That's an £8,432 balancing payment for 2025-26 on its own. But because this is a first return with a liability over £1,000, HMRC also collects a payment on account of half that amount — £4,216 — as an advance towards the 2026-27 tax year, due on the same 31 January 2027 date. Add the two together and the amount actually due on 31 January is £12,648, not £8,432.
| Illustrative sole trader, £45,000 profit, first Self Assessment return | Amount |
|---|---|
| Income tax on £32,430 at 20% | £6,486 |
| Class 4 National Insurance on £32,430 at 6% | £1,946 |
| 2025-26 balancing payment | £8,432 |
| Payment on account towards 2026-27 (50%) | £4,216 |
| Total due 31 January 2027 | £12,648 |
That's exactly the gap HMRC's "budget" tip is aimed at, and it's where starting now rather than in December has a real, calculable effect. HMRC's own Budget Payment Plan lets you pay a regular weekly or monthly amount into your account ahead of the bill, with whatever has built up set against it once it's calculated. Spread £12,648 over the roughly 16 weeks between now and 31 January 2027, and it's about £798 a week. Leave it until 1 December to start, with around nine weeks left, and the same total needs about £1,451 a week to clear. The bill doesn't change; what changes is how much of it has to come out of a single month's cashflow.
What it means depending on where you sit
If this is your first year filing, the worked example above is your real risk: the payment on account doubles what feels like "this year's tax" into something closer to two years' worth, landing on one date. That's the situation most worth starting a Budget Payment Plan for now, while there's still time for it to make a meaningful dent.
If you've filed for several years and already make payments on account, your January bill is usually just a smaller balancing adjustment, because most of the liability was already collected in January and July. The value of starting early is less dramatic in cash terms but still real: you find out sooner whether this year's balancing payment is higher or lower than the payments on account already made, rather than discovering a shortfall in the last week of January.
If you pay the High Income Child Benefit Charge, check the pre-populated Child Benefit figure against your own records before you file, particularly if your circumstances changed part-way through the year — a change of partner, or Child Benefit starting or stopping. And if you received the Winter Fuel Payment and your total income is over £35,000, build the clawback into what you expect to owe now, rather than being caught out by it in January.
What to do this week
Start by pulling together what you'll actually need: bank statements, invoices, any P60 or P11D, dividend vouchers and records of allowable expenses. If you're not sure whether you need to file at all this year, HMRC's own Self Assessment checker tool settles it in a few questions. Once you have a rough idea of what you'll owe, set up a Budget Payment Plan on GOV.UK so the money is building up before the bill lands, not after. We've written a complete guide to Self Assessment deadlines, payments on account and penalties if you want the fuller picture, and if you're not confident the figures are right, that's exactly what our Self Assessment service is for — we file it, we check the payment on account calculation, and we tell you the number in good time to budget for it.
What's still uncertain, and when we'll know
The rates and thresholds used in the worked example above are confirmed for the 2025-26 tax year being filed now. What isn't yet known is whether the Chancellor's Autumn Budget will change income tax, National Insurance or allowance thresholds for 2026-27, which would feed into next year's payment on account once HM Revenue and Customs recalculates it. That won't be clear until the Budget itself is delivered and the detail works through into HMRC's systems, so it's worth treating the £4,216 payment on account in the example as this year's figure, not a fixed number for next year too.