Self Assessment UK: Registration, Filing, Payments on Account and PenaltiesLast-Minute Self Assessment Tax Return — Filing Guide Before the Deadline
Rushing to file your Self Assessment? A step-by-step guide to submitting your tax return before the 31 January deadline, avoiding penalties, and what to do if you can't pay.
The Self Assessment deadline is approaching and you still haven’t filed. Here is exactly what to do, step by step, to get your return submitted and avoid penalties.
Read more: See our Self Assessment guide for a complete overview of this topic.
Key Deadlines
| Deadline | Date | Details |
|---|
| Tax year end | 5 April | End of the tax year being reported |
| Paper return deadline | 31 October | Must be received by HMRC by this date |
| Online return deadline | 31 January | Filing and payment due by midnight |
| Payment deadline | 31 January | Tax owed must be paid by this date |
| Second payment on account | 31 July | If applicable — 50% of estimated next year’s bill |
Late Filing Penalties
| How late | Penalty |
|---|
| 1 day late | £100 automatic penalty (even if no tax owed) |
| 3 months late | Additional £10 per day for up to 90 days (max £900) |
| 6 months late | Additional 5% of tax due or £300 (whichever is greater) |
| 12 months late | Additional 5% of tax due or £300 (whichever is greater) |
Late payment penalties are separate:
| How late (payment) | Penalty |
|---|
| 30 days late | 5% of tax unpaid |
| 6 months late | Additional 5% of tax unpaid |
| 12 months late | Additional 5% of tax unpaid |
Interest also accrues on all overdue tax at HMRC’s prevailing rate (currently 7.5% per year).
What You Need Before You Start
Gather these before logging in:
| Information | Where to find it |
|---|
| UTR (Unique Taxpayer Reference) | 10-digit number on your Self Assessment letters or previous returns |
| National Insurance number | Payslip, P60, or HMRC correspondence |
| P60 (employment income) | From your employer — issued by 31 May |
| P45 (if you left a job) | From your former employer |
| P11D (benefits in kind) | From your employer if applicable |
| Bank and building society interest statements | Annual interest certificate or check your account online |
| Dividend vouchers or statements | From investments or your own company |
| Self-employment income records | Invoices, bank statements, accounting records |
| Allowable expenses receipts or records | Keep for at least 5 years after the 31 January deadline |
| Gift Aid donations | Receipts or confirmations from charities |
| Pension contributions | Statements from pension provider |
| Student loan repayments | Payslip or SLC statement |
| Capital gains records | Purchase and sale records for shares, property, crypto |
| Rental income and expenses | Tenancy agreements, mortgage statements, repair receipts |
Step-by-Step: Filing Your Return Fast
Step 1 — Log In to HMRC
| Detail | Information |
|---|
| URL | tax.service.gov.uk |
| Login method | Government Gateway ID and password |
| Don’t have a Gateway ID? | You can register but it takes up to 10 working days to receive your activation code — if the deadline is days away, call HMRC on 0300 200 3310 |
| Forgotten password? | Reset online — you’ll need your email or phone number |
Step 2 — Employment Income
| What to enter | Source |
|---|
| Total pay from P60 | Box on your P60 labelled “Pay in this employment” |
| Tax deducted | Box labelled “Tax deducted” |
| Benefits in kind from P11D | Figures from your P11D if applicable |
If your employer gave you a P60 with an incorrect figure, enter the correct amount and contact your employer to issue a corrected P60.
Step 3 — Self-Employment Income
| Section | What to enter |
|---|
| Turnover | Total income before expenses |
| Expenses | Allowable business expenses (see table below) |
| Net profit | Turnover minus expenses |
Common allowable expenses (quick reference):
| Expense | Examples |
|---|
| Office costs | Stationery, phone bills, software subscriptions |
| Travel | Business mileage (45p/mile for first 10,000 miles), public transport |
| Working from home | £6/week flat rate or proportion of actual costs |
| Professional fees | Accountancy, legal, trade body memberships |
| Marketing | Website hosting, advertising, business cards |
| Insurance | Professional indemnity, public liability |
| Stock/materials | Goods purchased for resale or use in work |
Step 4 — Other Income
| Income type | Where it goes |
|---|
| Bank interest | Interest from banks and building societies |
| Dividends | Dividend income from shares or your own company |
| Rental income | UK property income (separate section) |
| Capital gains | Profits from selling assets (shares, property, crypto) |
| Foreign income | Income from overseas — may need to complete the foreign pages |
Step 5 — Claims and Reliefs
Don’t miss these — they reduce your tax bill:
| Relief | Value | Conditions |
|---|
| Personal Allowance | £12,570 | Already applied but check if reduced (over £100,000 income) |
| Marriage Allowance | Up to £252/year | Transfer 10% of Personal Allowance to spouse |
| Gift Aid | Extends basic rate band | Charitable donations — you claim the higher/additional rate relief |
| Pension contributions | Extends basic rate band | Personal pension contributions (not workplace salary sacrifice) |
| Working from home | £6/week flat rate | If your employer required you to work from home |
| Trading allowance | £1,000 | Side income under £1,000 is tax-free |
| Property allowance | £1,000 | Rental income under £1,000 is tax-free |
Step 6 — Review and Submit
| Check | Why |
|---|
| Review the tax calculation | HMRC shows your calculation before you submit — check the figures |
| Payments on account | You may owe payments on account for next year (50% of this year’s bill, paid 31 Jan and 31 Jul) |
| Reduce payments on account | If you expect lower income next year, you can reduce these — but get it wrong and you’ll face interest |
| Save a copy | Download or print your submitted return for your records |
What Your Tax Bill Looks Like (2025/26)
| Income band | Rate | Threshold |
|---|
| Personal Allowance | 0% | £0–£12,570 |
| Basic rate | 20% | £12,571–£50,270 |
| Higher rate | 40% | £50,271–£125,140 |
| Additional rate | 45% | Over £125,140 |
National Insurance (Class 4 — self-employed):
| Band | Rate | Threshold |
|---|
| Below Lower Profits Limit | 0% | £0–£12,570 |
| Between LPL and UPL | 6% | £12,571–£50,270 |
| Above UPL | 2% | Over £50,270 |
Class 2 NICs (£3.45/week) are collected through Self Assessment if profits exceed £12,570.
Can’t Pay Your Tax Bill?
| Option | Details |
|---|
| File on time anyway | Avoids the late filing penalty even if you can’t pay |
| Time to Pay arrangement | Spread payments over up to 12 months |
| Set up online | If your bill is under £30,000 — go to tax.service.gov.uk |
| Call HMRC | 0300 200 3310 for bills over £30,000 or complex circumstances |
| Interest charged | Currently 7.5% per year on the outstanding balance |
| Credit card | HMRC accepts credit card payments — but interest may be high |
See our HMRC Time to Pay guide for full details.
Common Mistakes That Delay Filing
| Mistake | How to fix it |
|---|
| Don’t have Government Gateway login | Register now at gov.uk — activation can take 10 working days |
| Lost UTR number | Call HMRC — 0300 200 3310 |
| Previous year’s return not filed | File the older return first, then file the current year |
| Waiting for a document | Use estimates if necessary and amend your return later (you have 12 months from the deadline to amend) |
| Not registered for Self Assessment | Register at gov.uk — this should have been done by 5 October |
Filing Checklist
| Task | Done? |
|---|
| Government Gateway login working | |
| UTR number to hand | |
| All P60s and P45s gathered | |
| Self-employment income and expenses calculated | |
| Bank interest and dividend figures checked | |
| Capital gains calculated (if any) | |
| Gift Aid and pension contributions noted | |
| Return submitted online | |
| Tax bill paid or Time to Pay arranged | |
| Copy of return saved | |
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