Who needs to file a Self Assessment tax return?

You must file if you are self-employed with income over £1,000, a company director who receives dividends, have rental income over £2,500, earn over £100,000, or are a CIS subcontractor. You should also file if you have untaxed income over £2,500 or are a partner in a business partnership.

When is the Self Assessment deadline?

The key deadlines are: register by 5 October (for new filers), paper return by 31 October, online return by 31 January, and first payment by 31 January. If you make payments on account, the second payment is due by 31 July.

What expenses can I claim on Self Assessment?

You can claim allowable business expenses including office costs, travel (45p/mile for first 10,000 miles by car), staff costs, marketing, professional fees, and financial costs. You cannot claim ordinary clothing, personal expenses, or fines.

What are payments on account?

Payments on account are advance payments towards your next tax bill, required when your Self Assessment bill exceeds £1,000 and less than 80% is collected at source. Each payment is 50% of your prior year tax bill, due 31 January and 31 July.

What are the penalties for late Self Assessment filing?

A £100 fixed penalty applies immediately on the day after the deadline, even if there is no tax to pay. After 3 months, daily £10 penalties accrue (up to £900). After 6 months, 5% of the tax due is added. After 12 months, a further 5% is charged. Interest accrues on unpaid tax from the due date.

HMRC Self Assessment: A Complete Guide for UK Business Owners | Yolist

Who needs to file a Self Assessment return?

You must register for Self Assessment and file a tax return if any of the following apply:

Sole traders — any self-employment income over £1,000 in the tax year
Business partners — all partners in a business partnership must file
Company directors — if you receive dividends or have untaxed income
Rental income — if your rental income exceeds £2,500 after allowable expenses
High earners — income over £100,000 (Personal Allowance tapering)
CIS subcontractors — to reclaim overpaid tax deducted under the Construction Industry Scheme
Other untaxed income — savings interest, foreign income, or tips over £2,500

Key dates and deadlines

Deadline	Date	What it covers
Register for Self Assessment	5 October	New filers must register by 5 Oct following the tax year end
Paper tax return	31 October	Must be received by HMRC (not just posted)
Online tax return	31 January	File your return online for the previous tax year
Pay your tax bill	31 January	Balancing payment + first payment on account
Second payment on account	31 July	Second instalment of advance payment

What you will need

Gather these documents before you start your return:

UTR (Unique Taxpayer Reference) — 10-digit number from HMRC, found on previous correspondence
National Insurance number
P60/P45 — if you also have employment income
Bank statements — 12 months of business bank records
Sales invoices — all income received in the tax year
Expense records — receipts, mileage logs, and supplier invoices
Previous year's return — useful for checking consistency and payments on account

Allowable expenses

You can deduct expenses that are “wholly and exclusively” for business purposes. Common allowable expenses include:

Office costs — stationery, printer ink, computer equipment, software
Travel and transport — business mileage (45p/mile for first 10,000 miles by car, 25p thereafter; 24p/mile for motorcycles; 20p/mile for bicycles)
Clothing — uniforms and protective clothing only; ordinary everyday clothing is not allowable
Staff costs — salaries, wages, employer NI, pension contributions
Marketing and advertising — website, print, online ads
Professional fees — accountant, solicitor, trade memberships
Financial costs — bank charges, business loan interest (landlords: restricted to basic rate relief from 2020)

Simplified expenses

HMRC allows some expenses to be calculated using flat rates, avoiding complex apportionment:

Working from home — £10/month (25–50 hours), £18/month (51–100 hours), £26/month (101+ hours)
Vehicle use — use the mileage rates above instead of claiming actual costs
Living at your business premises — flat rate deduction for private use, reducing the total expense claim

Note: You cannot switch between the actual cost method and simplified expenses for the same asset mid-year.

Payments on account

If your Self Assessment tax bill is over £1,000 and less than 80% of your tax is deducted at source, HMRC requires advance payments called payments on account:

Each payment equals 50% of your prior year's tax bill
First payment due: 31 January (same time as balancing payment)
Second payment due: 31 July
If your income has dropped, you can apply to reduce payments on account via your HMRC online account — but if you reduce too much, interest will be charged on the shortfall

Penalties for late filing or payment

1 day late — £100 fixed penalty (even if no tax is owed)
3 months late — £10/day penalty for up to 90 days (maximum £900)
6 months late — 5% of tax due or £300, whichever is greater
12 months late — further 5% of tax due or £300, whichever is greater
Late payment — interest charged from 31 January at the HMRC rate (currently Bank of England base rate + 2.5%)

Tips to reduce your Self Assessment bill

Pension contributions — personal pension contributions reduce your adjusted net income, potentially reinstating your Personal Allowance if you earn above £100k
Timing income — if you have flexibility, deferring invoices to the next tax year can delay the tax liability by 12 months
Claim all allowances — Annual Investment Allowance (up to £1 million) for equipment, Capital Allowances for vehicles
Marriage Allowance — transfer 10% of Personal Allowance to a spouse/civil partner if one earns under the threshold
Gift Aid — charitable donations via Gift Aid extend your basic rate band, beneficial for higher-rate taxpayers
Keep organised records— year-round bookkeeping means you won't miss deductible expenses at filing time

Use our free business calculators to estimate your tax liability.