If you’re self-employed or have a side hustle, the Self-Assessment deadline is probably already on your radar. 31 January 2026 - for filing your return and paying what you owe.
It can feel overwhelming, especially if it’s your first time. But most of the stress comes from leaving it too late or not knowing what you need. Start early, get organised, and you might even discover you’re owed money back. Particularly if you’re paying into a pension.
Who needs to file?
You’ll need to complete a Self-Assessment tax return if any of these apply to you:
Self-employment or side income - you earned more than £1,000 from self-employment, freelancing, or a side hustle.
Untaxed income - you received over £2,500 in untaxed income. This includes things like tips, commission, or freelance payments.
Rental income - you earned more than £1,000 from renting out property (or more than £7,500 if you’re renting out a room in your own home under the Rent a Room Scheme).
Savings and investment income - you received £10,000 or more from savings interest or dividends (excluding ISAs).
High Income Child Benefit Charge - you or your partner earn over £60,000 and you’re claiming Child Benefit.
Capital Gains Tax - you’ve sold assets like property or shares and need to pay Capital Gains Tax.
Pension tax relief - you’re a higher or additional rate taxpayer and want to claim extra tax relief on your pension contributions.
Unsure whether any of these apply to you? GOV.UK has a simple online tool that can help you check.
What you’ll need
Before you start your Self-Assessment, make sure you’ve got:
your 10-digit Unique Taxpayer Reference (UTR) - you’ll find this on letters from HMRC or in your Government Gateway account;
income records, invoices, bank statements, or anything showing what you earned during the tax year; and
work expenses receipts for things like equipment, software, and travel costs.
A few key details to keep in mind:
if your turnover is under £90,000, you can enter one total for expenses;
if it’s over £90,000, you’ll need to list expenses by type;
you can’t claim expenses if you’re using the £1,000 tax-free trading allowance - you have to pick one option; and
don’t forget your pension contribution details - this is where many people miss out on valuable tax relief.
The pension boost many people forget to claim
When you contribute to a personal pension, you’ll usually receive a 25% tax top up from the government. So if you pay in £100, HMRC effectively adds £25, bringing it to £125 in your pension.
If you earned over £50,270 in the 2024/25 tax year, you’re a higher rate taxpayer. That means you can claim an extra 20% back through your Self-Assessment.
Here’s what that looks like. Say you contributed £8,000 to your pension during 2024/25. Your provider will usually claim the basic rate of 20% on your behalf and top it up to £10,000. But you can claim another £2,000 back through your tax return. So your £10,000 pension contribution actually cost you £6,000.
Most people don’t realise this. And HMRC won’t remind you.
How to claim it
When you’re filling in your Self-Assessment, look for the pension contributions section in form SA100. It asks for “payments into a registered pension scheme, annuity contract, or employer’s scheme where deductions were made after tax.”
Enter the gross amount - that’s the total including the 20% your provider already added. In our example above, you’d enter £10,000, not the £8,000 you paid.
The system works out your additional relief automatically. You’ll either get a refund or your next tax bill will be reduced.
You don’t need to send proof when you file, but keep your pension statements for at least five years in case HMRC asks later. And if you’ve missed claiming in previous years, you can backdate for up to four years.
Understanding payments on account
If your last tax bill was over £1,000, you’ll usually need to make payments on account - unless you paid more than 80% of your tax through PAYE or at source. These are payments made twice a year:
- on 31 January; and
- on 31 July.
And each payment is half of your previous year’s bill.
So if your 2023/24 bill was £3,000, you’ll have made two payments of £1,500 during 2024/25. When you file in January 2026, those get deducted. If your new bill is £4,000, you’ll pay £1,000 as a balancing payment, plus £2,000 as your first payment on account for 2025/26.
It works very differently from PAYE, where tax comes out monthly. Most self-employed people set aside 20-30% of their income to stay on top of it.
What if you can’t pay?
If you’re struggling, contact HMRC on 0300 200 3820 as soon as possible. They might offer more time to pay, a payment plan, or the Time to Pay service for bills under £30,000.
Don’t ignore it. HMRC can take enforcement action, including taking money directly from your earnings, bank account or pension.
Final thoughts
Self-Assessment doesn’t have to be a headache. With a bit of prep and the right paperwork, you can make it straightforward - and even spot opportunities to save. Don’t forget to claim everything you’re entitled to, especially your pension tax relief.
A little effort now means more money working for your future, right where it belongs.
Please note that tax rules change regularly, and the actual tax benefits you receive will depend on your individual circumstances. If you’re not sure, please seek professional advice.
