Tax

Last-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.

· 6 min read

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.

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