Self Assessment Deadlines and Payments on Account UK 2025/26

Missing a self assessment deadline costs you money from day one. HMRC charges automatic penalties for late filing starting at £100, and late payment interest accrues daily. If you are newly self-employed, the deadline system can seem baffling: you are paying tax for the previous year, making advance payments for the current year, and somehow need to have enough cash ready by 31 January, which is traditionally the most expensive month of the year.

This guide maps every key self assessment date for 2025/26, explains payments on account, and sets out what happens if you miss a deadline. Use our self-employed tax calculator to estimate your January bill so you can prepare well before the due date.

The UK tax year and key dates

The UK tax year runs from 6 April to 5 April. The 2025/26 tax year covers earnings from 6 April 2025 to 5 April 2026. Your self assessment return for this period must be filed and paid by midnight on 31 January 2027. That is nearly ten months after the tax year ends, which gives you time to gather records but also creates a gap where many taxpayers forget to set money aside.

Filing deadlines: paper vs online

Paper self assessment returns (SA100) must reach HMRC by 31 October following the tax year end. Almost nobody uses paper filing anymore. Online filing through HMRC's portal or compatible software extends the deadline to 31 January. For 2025/26, the online deadline is 31 January 2027. Filing online also gives you an instant calculation of your tax bill and allows you to amend the return within 12 months of the filing deadline if you discover errors.

If you miss the 31 January deadline, an automatic late filing penalty of £100 applies immediately, even if you owe no tax. Further penalties escalate: after three months, £10 per day is charged for up to 90 days. After six months, the higher of £300 or 5% of the tax due is added. After twelve months, another 5% charge applies. These penalties are on top of interest on any unpaid tax.

Payments on account explained

Payments on account are HMRC's way of collecting tax during the year rather than in one lump sum. If your previous year's self assessment bill exceeded £1,000 and less than 80% of your total tax was collected through PAYE, you must make two advance payments: one by 31 January and one by 31 July. Each payment on account is 50% of the previous year's total bill (including Class 4 NI).

Here is how the cycle works in practice. Suppose your 2024/25 self assessment bill (calculated in January 2026) is £8,000. You pay £8,000 by 31 January 2026 (the balancing payment for 2024/25). HMRC then requires two payments on account for 2025/26: £4,000 by 31 January 2026 and £4,000 by 31 July 2026. When you file your 2025/26 return in January 2027, you pay the difference between what you have already paid (£8,000) and what you actually owe. If you owe £9,000, the balancing payment is £1,000. If you owe £7,000, you receive a £1,000 refund.

Estimate your upcoming bill with our self-employed tax calculator so your payments on account do not catch you off guard.

Reducing payments on account

If you expect your next year's profits to be significantly lower, you can apply to reduce your payments on account through your HMRC online account or by submitting form SA303. Reducing them too aggressively triggers interest charges if your actual bill turns out higher than the reduced payments. Only reduce if you have a genuine reason, such as losing a major client, taking a career break, or winding down the business.

Conversely, if your profits are rising sharply, your payments on account (based on last year) may not cover the actual bill, and you will face a larger balancing payment in January. Planning for this is essential. A freelancer whose profit jumps from £35,000 to £55,000 could see their tax bill rise by roughly £5,000 to £6,000 while payments on account remain at the old level.

Payment methods accepted by HMRC

• Online bank transfer (Faster Payments, allow 3 to 5 working days)
• Debit or corporate credit card (fee applies for personal credit cards)
• Direct Debit (Budget Payment Plan for regular instalments)
• At your bank using a paying-in slip (allow 3 working days)
• CHAPS same-day transfer for urgent payments

Penalties and interest for late payment

Late payment interest is charged from the day after the deadline at the Bank of England base rate plus 2.5%. For mid-2025, that is roughly 7.25% to 7.75% annually. On a £5,000 overdue bill, that is approximately £1 per day in interest. HMRC also charges a late payment penalty of 5% of the unpaid tax if it remains outstanding 30 days after the deadline, with further 5% penalties at six and twelve months.

If you cannot pay in full by 31 January, contact HMRC as soon as possible to set up a Time to Pay arrangement. This spreads the bill over monthly instalments, typically up to 12 months. Interest still applies, but you avoid the penalty charges that come with simply ignoring the deadline. HMRC is generally more flexible if you contact them before the due date rather than after.

First-year self-employed: what to expect

Your first self assessment year is the simplest for payments. You file once, pay once by 31 January, and no payments on account are required because there is no prior year bill to base them on. The challenge is that you are paying tax on a full year of profits in a single payment, which can be a large sum if you have not been setting money aside. Treat that first January payment as a lesson in cash flow discipline for every year that follows.

From your second year onwards, the payment cycle accelerates. You are paying the balancing amount for year one, plus the first payment on account for year two, all on the same 31 January. This double hit (often called the January spike) catches many new freelancers off guard. A first-year bill of £6,000 means your second January payment could be £9,000 (the £6,000 balancing payment plus a £3,000 payment on account). Budget for it from day one and you will never be caught short.

For a full overview of what sole traders owe, see our self-employed tax guide. For Class 4 NI specifics, read our Class 4 National Insurance guide. Use our self-employed tax calculator to forecast every payment before it is due, and mark 31 January and 31 July in your calendar as non-negotiable dates.

Making Tax Digital quarterly updates

From April 2026, self-employed individuals and landlords with gross income above £50,000 must comply with Making Tax Digital for Income Tax Self Assessment (MTD ITSA). This requires keeping digital records and submitting quarterly summary updates to HMRC, in addition to the annual self assessment return. From April 2027, the threshold drops to £30,000. Quarterly updates report total income and total expenses for each three-month period. They are not tax calculations and do not trigger a payment demand.

Compatible software includes FreeAgent, Xero, QuickBooks, Sage and several others listed on gov.uk. If you currently keep records in a spreadsheet, you will need to migrate to qualifying software before the deadline. The annual self assessment return still happens, and the January 31 payment deadline remains unchanged. MTD adds reporting frequency, not new tax charges.

Amending a return and claiming refunds

If you discover an error after filing, you can amend your online return within 12 months of the original filing deadline. For a 2025/26 return filed by 31 January 2027, amendments are accepted until 31 January 2028. Amendments made after 12 months require a formal claim or correspondence with HMRC. Overpaid tax from previous years can be reclaimed by amending the relevant return or writing to HMRC with evidence.

Common reasons for amendments include missed expense claims, corrected dividend figures from a company, updated pension contribution amounts, and revised property income after discovering allowable costs that were initially overlooked. Each amendment recalculates your tax and NI, and any refund is paid by bank transfer or applied against future liabilities. Keep copies of every amended return and the confirmation from HMRC showing the revised calculation.

Missing a deadline is expensive, but HMRC is generally reasonable if you communicate early. Set calendar reminders for 5 October (registration), 31 January (filing and payment), and 31 July (second payment on account). Diarise them a month in advance so you have time to gather records, complete your return, and fund the payment before the due date arrives. A missed deadline costs far more in penalties than an hour spent setting reminders.