Self Assessment for Freelancers: Deadlines, Expenses & How to Prepare

For freelancers, Self Assessment is how you tell HMRC what you earned and pay the tax on it. It has a reputation for being stressful — but almost all of that stress comes from leaving it late and scrambling for records in January. Prepare a little through the year and it becomes routine. Here's what to know: the key dates, how payments on account work, what you can claim, and the records that make it painless.

This is general information, not tax advice — check GOV.UK or speak to an accountant for your situation.

The Key Dates

The UK tax year runs 6 April to 5 April. For each tax year you have:

• 5 October — deadline to register for Self Assessment if it's your first year (see our guide to registering as self-employed).
• 31 October — deadline to file a paper tax return.
• 31 January — deadline to file online and, crucially, to pay the tax you owe for the previous tax year.

So for the 2025/26 tax year (ending 5 April 2026), you file and pay online by 31 January 2027. Miss the filing deadline and there's an automatic £100 penalty even if you owe nothing, with more added the longer you leave it.

Payments on Account (the Surprise to Plan For)

The detail that catches first-time filers out: payments on account. If your tax bill is over £1,000, HMRC asks you to pre-pay towards next year's tax in two instalments — each 50% of last year's bill — due 31 January and 31 July.

In practice, in your first profitable year you can face 1.5 times the tax you expected on that 31 January: the full bill for the year just gone, plus the first 50% payment on account for the year ahead. It's not extra tax — it's paid in advance — but it's a real cash-flow hit if you haven't set money aside. Plan for it.

Allowable Expenses

You pay tax on your profit — income minus allowable business expenses — so claiming everything you're entitled to legitimately lowers your bill. Common allowable expenses for freelancers include:

• Office costs — stationery, software subscriptions, phone and internet (business portion).
• Equipment — computers, tools and gear used for work.
• Travel — business mileage (see the mileage calculator), public transport, parking — not your normal commute.
• Working from home — a proportion of household costs, or HMRC's simplified flat rate.
• Professional costs — accountancy fees, business insurance, relevant training, bank charges on a business account.
• Marketing — website, advertising and similar costs.

Expenses must be wholly and exclusively for the business. Keep a receipt for everything you claim.

The Records to Keep

You must keep records of income and expenses (generally for at least five years after the 31 January deadline). The freelancers who breeze through Self Assessment are simply the ones who kept good records all year:

• Every invoice you issued — your income, evidenced.
• Every business receipt — your expenses, evidenced.
• Bank statements, ideally from a separate business account.
• A running total of income and costs, updated as you go.

This is where clean invoicing pays off twice. With 1nvoic3 your invoices are created and stored as you go, and you can export your full history — so when January comes, your income figure is already totalled and your records are in one place rather than scattered across emails.

Common Mistakes to Avoid

1. Leaving it to January. The deadline rush causes errors and stress. File earlier — you still don't pay until 31 January.
2. Not setting tax money aside. Put a percentage of every payment in a separate pot from day one so the bill (and payments on account) doesn't hurt.
3. Forgetting payments on account. Budget for that potential 1.5x first bill.
4. Missing expenses. Unclaimed costs mean tax overpaid. Track them all year.
5. No records. Reconstructing a year from memory is painful and risky. Keep evidence as you go.

Frequently Asked Questions

When is the Self Assessment deadline? File online and pay by 31 January following the end of the tax year (5 April). Paper returns are due by 31 October. First-time filers must also register by 5 October.

What are payments on account? Advance payments towards next year's tax, each 50% of your last bill, due 31 January and 31 July — triggered when your tax bill is over £1,000. It can make your first January bill about 1.5 times what you expected.

What expenses can freelancers claim? Costs incurred wholly and exclusively for the business — software, equipment, business travel, a portion of home and phone costs, accountancy fees, insurance and marketing. Keep a receipt for each.

How long should I keep my records? Generally at least five years after the 31 January submission deadline for that tax year. Keep copies of invoices, receipts and bank records.

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Estimate your bill with the free self-employed tax calculator, and keep clean income records by invoicing with 1nvoic3 — free, no sign-up. See also how to register as self-employed and how to invoice as a sole trader.