Self Assessment deadlines: 2026/27
Self Assessment Deadlines & Payments on Account 2026/27
Complete guide to UK Self Assessment filing + payment timelines for 2026/27. 31 January online filing deadline, 31 October paper deadline, Payments on Account 50%/50% mechanics, "year 1 cash flow shock" of going self-employed, late filing penalties (£100 + £10/day + 5% × 2), late payment surcharges (5% × 3), Time-to-Pay arrangements, SA303 POA reduction, HMRC enquiry windows, 3 worked taxpayer scenarios.
2026/27 SA timeline
| Date | What's due | Who pays |
|---|---|---|
| 5 Oct 2027 | Registration deadline for 2026/27 first-time SA filers | New self-employed, new HICBC, new rental income |
| 31 Oct 2027 | Paper return deadline (rarely used) | All SA filers using paper SA100 |
| 31 Jan 2028 | Online filing + 2026/27 balancing payment + 2027/28 first POA | All SA filers (most common deadline) |
| 31 Jul 2028 | 2027/28 second POA | SA filers above POA threshold |
| 31 Jan 2029 | 2027/28 filing + balancing + 2028/29 first POA | Next annual cycle |
Payments on Account mechanics
POAs are advance payments toward NEXT year's tax bill. Triggered when:
- Your total tax liability (after PAYE) exceeds £1,000; AND
- Less than 80% of your total tax was deducted at source via PAYE
Each POA = 50% of last year's liability (excluding CGT and Class 2 NI). First POA due 31 January (same day as the prior year's balancing payment - this is the cash-flow shock). Second POA due 31 July. Difference reconciled at the NEXT 31 January when actual liability is determined.
3 worked taxpayer scenarios
| Taxpayer | Tax liability | PAYE paid | SA balance | POA req? | Due 31 Jan | Due 31 Jul |
|---|---|---|---|---|---|---|
| Employee with side income, year 1 First SA year - balancing payment + first POA both due same day. Cash-flow shock. | £3,500 | £1,200 | £2,300 | YES | £3,450 | £1,150 |
| Established self-employed Pure SA. Balancing payment + first POA due 31 Jan 2028. Second POA 31 Jul 2028. | £8,000 | £0 | £8,000 | YES | £12,000 | £4,000 |
| PAYE-heavy with small side income Tax bill under £1k threshold + PAYE covers 75% → POA EXEMPT. Just pay balancing amount. | £800 | £600 | £200 | NO | £200 | £0 |
Late filing + late payment penalty escalator
Late filing penalties
- Day 1 after deadline: £100 fixed
- After 3 months: £10/day daily penalty (max 90 days = £900)
- After 6 months: £300 OR 5% of tax due (whichever higher)
- After 12 months: same £300 OR 5% AGAIN
- Worst case 13+ months late: £1600+ minimum
Late payment penalties
- 30 days late: 5% surcharge on unpaid tax
- 6 months late: 5% surcharge again
- 12 months late: 5% surcharge AGAIN
- Plus daily interest: 7.50% per annum on unpaid amount from original due date
- Worst case 13+ months late: ~15% surcharge + 8% interest = ~23% extra cost
Filing and payment penalties are CUMULATIVE - you can be charged both for the same period. Reasonable excuse defence (illness, bereavement, HMRC system failure) can be used to appeal but NOT accepted: "I forgot", "I didn't have the money", "my accountant is dealing with it".
Time-to-Pay arrangements
HMRC's instalment plan lets you spread tax payments over up to 12 months (sometimes longer for substantial debts). Apply online via HMRC's "Self-Serve Time-to-Pay" service if your debt is under £30,000 and you have no other tax debts. Above £30,000 or with other debts: call HMRC Debt Management.
- Apply BEFORE the due date: skip the 5% late-payment surcharge entirely
- Apply within 30 days after due date: HMRC may still waive the surcharge if you're cooperative
- Interest accrues at 7.5% prescribed rate throughout the arrangement
- Missing a Time-to-Pay instalment collapses the arrangement: full balance due immediately + collection action
- Reliable payment record makes future Time-to-Pay arrangements much easier to renew
Frequently asked questions
When is the Self Assessment deadline for 2026/27?
Two filing deadlines depending on format. Online filing: 31 January 2028 for the 2026/27 tax year (6 April 2026 - 5 April 2027). Paper filing: 31 October 2027 for the same tax year (rarely used - HMRC phased out paper forms from 2024 except for limited circumstances). Both balancing payment + first POA for next year are due 31 January 2028 alongside the online filing deadline. Second POA for 2027/28 due 31 July 2028. Online filing requires registration with HMRC's Government Gateway service - allow 10 working days to receive activation code if first-time filer. The 31 January deadline has been fixed since 2008 (was 30 September for paper / 31 January for electronic pre-2008). Late-filing penalty starts the day after the deadline regardless of whether tax is actually owed.
What are "Payments on Account" and do I have to pay them?
Payments on Account (POA) are advance payments toward NEXT year's tax bill, paid in two instalments. Section 59A Taxes Management Act 1970. Triggered if: your total tax liability (after PAYE deductions) exceeds £1,000 AND less than 80% of your total tax was deducted at source via PAYE. Each POA: 50% of your previous year's tax liability (excluding CGT and Class 2 NI). First POA: due 31 January (same day as the prior-year balancing payment - the "cash-flow shock" of year 1). Second POA: due 31 July. Reconciliation: at the following 31 January, when you file the actual SA for the year, any difference between paid POAs + balancing payment vs actual liability is settled. If you overpaid POAs you get a refund; underpaid you pay the difference. POAs are how HMRC keeps cash flowing in - the system effectively keeps you paying tax 7-8 months in advance throughout self-employment.
What is the "year 1 cash flow shock" of going self-employed?
On 31 January of your second year of self-employment, you owe: (a) the full balancing payment for year 1's tax (no POAs were paid against this), PLUS (b) the first POA for year 2's tax (50% of year 1's liability). So a self-employed person with £10k tax bill in year 1 owes £15k on 31 January of year 2 (£10k balancing + £5k first POA). Then £5k more on 31 July of year 2 (second POA). Total £20k in 6 months for what looks like "one year" of tax. From year 3 onwards the cash flow stabilises: each year you pay ~£10k on 31 Jan (balancing for prior year + first POA for current) and ~£5k on 31 Jul. Major reason new self-employed go bankrupt - they didn't budget for the year-2 shock. Mitigation: set aside ~30% of every invoice into a separate tax savings account from day 1. Pension contributions reduce taxable income and can be claimed even after year-end on the SA, providing year-1 cushion.
How are POAs calculated exactly?
Two POAs each year = 50% of your PREVIOUS year's tax liability (after PAYE deductions but BEFORE Class 2 NI and CGT). Worked example: 2025/26 SA filed in Jan 2027 shows £12,000 of tax + £200 Class 2 NI + £600 CGT = £12,800 total. POA base = £12,000 (excludes Class 2 NI + CGT). Each POA = £6,000. First POA due 31 Jan 2028 alongside any 2025/26 balancing. Second POA due 31 Jul 2028. Both POAs offset against 2026/27 final liability when filed Jan 2029. POAs are based on the FILED year, not the latest. So 2027/28 POAs are based on the 2025/26 filing (the most recent completed return at the time of the 31 Jan 2027 / 31 Jul 2027 due dates). Newly-self-employed in 2026/27: no POAs in their first SA cycle because there's no prior year liability to base it on. Established self-employed: POAs always based on prior year unless reduced via SA303.
Can I reduce my POAs?
Yes via Form SA303 - "Claim to reduce payments on account". Use when you expect this year's tax bill to be LOWER than last year's (lower income, more pension contributions, retirement, business slowdown). File SA303 BEFORE the POA due date - typically submitted with the prior year's SA return or via the online HMRC account. HMRC accepts the reduction at face value but reserves the right to charge interest if the reduction was excessive. If reduction is too low: the underpayment plus interest from the original due date is charged. If reduction is reasonable: no penalty. If you didn't reduce when you could have: not a penalty, but you've effectively given HMRC a free loan. SA303 is genuinely useful for: business owners with declining revenue, people retiring mid-year, contractors moving from outside-IR35 to inside-IR35 (PAYE coverage rises). DON'T use to delay tax you actually owe - HMRC will charge interest + potentially a "deliberate inaccuracy" penalty.
What happens if I miss the 31 January deadline?
Penalty escalates over time. Section 9 + Schedule 55 FA 2009. £100 immediate fixed penalty the day after the deadline, regardless of whether tax is owed. £10/day after 3 months (so up to £900 of daily penalties before the 6-month point). £300 or 5% of tax due (whichever higher) at 6 months late. £300 or 5% of tax due (whichever higher) again at 12 months late. Worked example: filing 13 months late (1 March 2029 for 2026/27 return): £100 + (£10 × 90 days, capped) = £900 + £300 (6 months) + £300 (12 months) = £1,600 minimum penalty, even if your tax bill was zero. If your tax bill was £20k, the 5% penalty at 6/12 months becomes £1,000 each = £100 + £900 + £1,000 + £1,000 = £3,000 in penalties. "Reasonable excuse" defence can be used to appeal: serious illness, bereavement of close family member, postal delay (with proof), HMRC system failure. NOT accepted: "I forgot", "I didn't have the money", "my accountant is dealing with it".
What about late PAYMENT penalties separate from late filing?
Different scheme, also escalates. Section 59C + Schedule 56 FA 2009. 5% surcharge at 30 days late. 5% surcharge at 6 months late. 5% surcharge at 12 months late. Plus daily interest at HMRC's prescribed rate (currently 7.50% per annum, set quarterly) from the original due date. Worked example: £5,000 tax owed, paid 7 months late. Surcharges: £250 (30 days) + £250 (6 months) = £500. Interest at 7.5%: £5,000 × 7.5% × 7/12 = £219. Total late payment cost: £719 on top of the original £5,000 = ~14% effective penalty. Late payment penalties are CUMULATIVE with late filing penalties - you can be charged both for the same period. The only way to escape: Time-to-Pay arrangement agreed with HMRC BEFORE the due date.
What is a Time-to-Pay arrangement?
An HMRC-approved instalment plan letting you spread tax payments over up to 12 months (sometimes longer for substantial debts). Section 108 TMA 1970. Apply via HMRC online if your debt is under £30,000 and you have no other tax debts (the automated "Self-Serve Time-to-Pay" service). Above £30,000 or with other debts: call HMRC and speak to the Debt Management team. Approval typically takes 1-3 weeks. Key benefits: monthly payments instead of lump sum, no late payment 5% surcharge IF the arrangement is agreed BEFORE the original due date (or within 30 days after). Costs: interest still accrues at 7.5% prescribed rate, but no surcharge. Typical terms: 12 months for under £30k debt, 24-36 months for larger debts with hardship justification. Failure rate: if you miss a Time-to-Pay instalment, the full arrangement collapses and HMRC moves to collection (debt collection agency referral, court action, asset seizure). Reliable payment record makes Time-to-Pay much easier to renew next year if needed.
When do I have to register for Self Assessment?
By 5 October following the end of the tax year in which the registration trigger occurred. Triggers include: self-employed trading profit, rental income £2,500+ gross, untaxed savings/investment income above PSA, any capital gain over the £3k AEA, dividend income above £500, foreign income £2,000+, Child Benefit and household income over £60k (HICBC), being a company director with non-PAYE income, sole trader registration, partnership registration. Register at gov.uk/register-for-self-assessment. HMRC issues a Unique Tax Reference (UTR) within 10 working days. Penalty for missing 5 October registration deadline: £100 fixed + 5%/10%/30% of tax due depending on disclosure timing (careless / deliberate / deliberate-and-concealed). HMRC's "failure to notify" is one of the highest-enforcement areas, particularly post-2024 with platform reporting (eBay/Vinted/Etsy/Airbnb sharing data with HMRC since January 2024).
Can I file SA myself or do I need an accountant?
Most employees + simple-self-employed can file themselves via HMRC online. Standard cases: salaried income only with HICBC, rental property with simple letting, side hustle under £20k, freelance consultant with one income stream. Use an accountant for: limited company directors (different return - CT600), partnership returns, complex CGT (multiple disposals, property sales), R&D credits, complex offshore income, multiple income sources interacting with student loan / pension AA / SEIS. Accountant fees typically £300-1,500/year for individuals, £600-3,000 for self-employed, £1,500-5,000 for owner-managed companies. HMRC's online form is free but the value of an accountant is mostly: catching deductions you'd miss, planning ahead, and providing audit defence if HMRC enquires. SA tax software (FreeAgent, Xero Self Assessment, TaxCalc) sits between DIY and accountant - £80-200/year guides you through the return with built-in checks.
How long does HMRC have to enquire into my SA?
Section 9A TMA 1970 enquiry windows. Standard cases: 12 months from the date HMRC RECEIVED your return (if filed on time) or from 31 January (if filed late). So a 2026/27 SA filed 30 January 2028 can be enquired into until 30 January 2029. Careless inaccuracy: 4 years from the end of the relevant tax year (so 6 April 2031 for 2026/27 with careless errors). Deliberate inaccuracy: 20 years from the end of the tax year (so 6 April 2047 for 2026/27 with deliberate concealment). "Discovery" assessment: HMRC can re-open an old return if they DISCOVER new information they couldn't reasonably have known earlier - typically used when they receive third-party data later (foreign bank account, platform sales). Discovery cases follow the careless/deliberate timeline. Recommendation: keep ALL supporting records for 6 years minimum (HMRC standard); for any complex / high-value items, 20 years.
What if I overpaid - can I claim a refund?
Yes, two routes. SA refund: file your SA showing you overpaid (e.g. PAYE deducted more than your final liability). HMRC refunds within 2-6 weeks via BACS or cheque to your nominated account. Faster if you submit bank details. The refund includes interest at HMRC's prescribed repayment rate (currently lower than the prescribed underpayment rate - typically 4-5% vs 7.5%). R40 refund (non-SA): if you're not in SA but have overpaid tax via PAYE / on savings, use Form R40. Typical case: bank interest had 20% deducted but you're a non-taxpayer; pension lump sum was over-taxed via emergency code. R40 processed in 6-8 weeks. Time limit: 4 years from end of relevant tax year (so claim 2022/23 overpayment by 5 April 2027). After 4 years, refund is generally lost. Repayment supplement: HMRC pays interest on refunds delayed beyond the statutory window, but it's modest (~3-4% per annum).
Related deadlines + planning guides
- UK tax deadlines 2026 - all key dates across SA, CT, VAT, PAYE.
- Self Assessment step-by-step - filing walkthrough.
- UK tax calendar 2026/27 - month-by-month tax events.
- Tax year-end checklist (5 April) - what to do before the tax year closes.
- HMRC penalties guide - full penalty regime across all UK taxes.
- HMRC tax investigation guide - what happens if HMRC opens an enquiry.
- MTD ITSA guide - quarterly reporting for self-employed/landlord over £50k from April 2026.
- Side hustle tax calculator - when side income triggers SA registration.