Self-Assessment Tax Return: A Simple Guide for Freelancers and Side Hustlers

If you earn money on the side — a few client projects, a stall at the weekend market, some tutoring, a car full of deliveries — the tax deadline has a way of arriving faster than you expect. January feels like a long way off in July. It isn't.

Self Assessment isn't complicated once you strip it back. There are four things worth knowing: whether you have to file, by when, what you can deduct, and why HMRC sometimes asks for money twice in the same year. Sort those out and the whole thing becomes an hour of admin rather than a small annual crisis.

Who actually needs to file

HMRC expects a return from you if it has asked for one, or if you have income that hasn't been taxed at source and it crosses certain thresholds. For freelancers and side hustlers, the usual triggers are:

• You earned more than £1,000 from self-employment in a tax year — that covers freelance work, consultancy alongside a job, selling things you've made, tutoring, delivery driving and casual gigs.
• You rent out property and the income is above the property allowance.
• You received dividends, savings interest or foreign income above the relevant allowances.
• You owe the High Income Child Benefit Charge.
• You sold shares, a second property or other assets and made a gain above your annual exemption.

That £1,000 figure is the trading allowance. Below it, a small side hustle usually doesn't need to be reported at all. Cross it, though, and you need to register — even if your actual profit is tiny, because the allowance is an alternative to claiming expenses, not an extra layer on top of them.

One more thing worth knowing: if the tax you owe is small and you also have a job, HMRC can sometimes collect it through your tax code instead of asking for a lump sum. It's worth asking.

The four dates to put in your diary

1. 5 October — deadline to register for Self Assessment, if this is your first return for that tax year.
2. 31 October — deadline for a paper return. Most people file online, so treat this as the last-chance date for posting forms.
3. 31 January — online return and payment deadline for the previous tax year, plus any first payment on account.
4. 31 July — second payment on account.

Miss the filing deadline and a £100 penalty lands almost immediately, with further charges stacking up the longer you leave it. Interest also runs on unpaid tax. If you're going to miss a deadline, file anyway: the penalty for filing late is separate from the penalty for paying late, and a return with an estimated figure is better than nothing.

What you can legitimately claim

Expenses reduce your profit, and profit is what you're taxed on. The test HMRC applies is whether a cost was incurred wholly and exclusively for the business. Typical claims for someone working for themselves:

• Software, subscriptions, hosting and domain names
• Phone and broadband — the business share, not the whole bill
• Equipment, materials, stationery and postage
• Travel to clients, plus mileage if you drive: HMRC's simplified rate is 45p per mile for the first 10,000 business miles, then 25p
• Professional fees, business insurance and bank charges on a business account
• Marketing, advertising and website costs
• Training that updates skills you already use

Where people get caught out

Client entertaining isn't allowable in the UK, however useful the lunch felt at the time. Ordinary clothing isn't either, unless it's a uniform or protective kit. Fines are never deductible, and neither is the tax itself. Personal spending run through a business account doesn't become a business expense just because the card said "business".

If something is part business and part personal, claim the business proportion and be ready to explain how you worked it out. Round numbers with no method behind them are what attract questions.

Keeping records without the dread

A separate bank account does more for your sanity than any app. Funnel business income and spending through it, photograph receipts as they happen, and keep a simple spreadsheet of invoices and costs. You need to keep records for at least five years after the 31 January filing deadline for that tax year, so don't bin anything in a spring clean.

Payment on account: the January surprise

If your tax bill is over £1,000 and less than 80% of your tax was collected at source, HMRC asks you to pay in instalments — half now, half later — towards the following year.

Here's how that feels in practice. Say your first year's profit produces a £4,000 bill. By 31 January you pay that £4,000, plus a first payment on account of £2,000. By 31 July, another £2,000 goes out. Your first January is therefore double what you were expecting, which is why so many new freelancers get a nasty shock.

If your profits are falling, you can apply to reduce your payments on account. Do it only if you're confident, because if you reduce them too far you'll pay interest on the shortfall.

A routine that keeps January boring

Move a set percentage of every payment you receive into a separate tax pot the day it arrives — somewhere between 20% and 30% is a sensible starting point, depending on your income and whether National Insurance is also due. Spend twenty minutes at the end of each month tidying receipts and updating your figures. File in May or June, when the previous year's records are still fresh and you have months of breathing room. And if your income is messy — property, overseas work, share schemes, big equipment purchases — pay an accountant. Their fee is usually cheaper than the mistakes you'd make alone.

This is general information, not tax advice. Rules and thresholds change, and your circumstances are your own — check the current guidance on GOV.UK or speak to a qualified accountant before you file.

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