Self Assessment

Self Assessment for sole traders and CIS subbies: deadlines, payments on account, penalties, CIS refunds and expenses, checked against GOV.UK.

If you work for yourself, your 2025/26 tax return and bill are due by 31 January 2027. These guides answer the questions sole traders and CIS subcontractors ask most: what the dates are, why January's bill includes payments on account, what penalties cost, how to get CIS back, and what to do if you can't pay.

Every figure was checked against GOV.UK on 23 October 2026. They are general information, not tax advice. Start with the January tax bill calculator to see your own numbers.

Where to start

Self Assessment deadline 31 January 2027: every date for the 2025/26 tax year: Every key date for the 2025/26 return.
January tax bill calculator: what you'll pay on 31 January 2027: Estimate your 31 January and 31 July payments.
Payments on account explained: why January's bill is so big: Why January's bill is bigger than you expected.
Getting a CIS refund through your Self Assessment return, step by step: Getting CIS deductions back, step by step.
Self Assessment records checklist for sole traders and subbies: Everything to gather before you file.

All guides in Self Assessment

Self Assessment deadline 31 January 2027: every date for the 2025/26 tax yearIf you were self-employed between 6 April 2025 and 5 April 2026, your online tax return and any tax you owe are due by 11:59pm on 31 January 2027. Here are the dates that matter and what to do now so January isn't a scramble.603 words Self Assessment late filing penalties: how the £100 penalty growsA late tax return costs £100 the day after the deadline, even if you owe nothing. Leave it longer and the penalties stack up. Here's how GOV.UK says they build, with worked examples.460 words Paying Self Assessment late: penalties and interest explainedPaying tax late costs money in two ways: a 5% penalty at set points, and interest for every day it's unpaid. Here's how both work for the 2025/26 bill due on 31 January 2027.434 words Payments on account explained: why January's bill is so bigPayments on account are advance payments towards next year's tax bill. Each is usually half of last year's bill, paid on 31 January and 31 July. They're why many first-year sole traders find January's bill is 50% bigger than...501 words Your first Self Assessment tax bill: what you'll pay and whenIn your first year self-employed nobody takes tax from your pay, so the whole bill lands at once, and January usually asks for half of next year's bill in advance too. Here's what to expect, with real 2025/26 figures.516 words Getting a CIS refund through your Self Assessment return, step by stepIf contractors took 20% or 30% off your labour all year, you've probably paid more tax than you owe. As a sole trader, you get it back through your Self Assessment return. Here's the process for 2025/26, with a worked example.503 words What expenses can CIS subcontractors and tradespeople claim?Every pound of allowable expenses cuts your taxable profit, and for a CIS subbie that usually means a bigger refund. Here's what GOV.UK says the self-employed can claim, applied to the costs builders actually have.458 words Claiming mileage when self-employed: the 2025/26 and 2026/27 ratesIf you drive a van or car for work, you can claim a flat rate per business mile instead of working out actual running costs. The rate changed on 6 April 2026, so your 2025/26 return and next year's use different figures.415 words Use of home as office allowance for the self-employedDoing quotes, invoices and admin from home lets you claim some household costs. Most tradespeople use HMRC's flat rate, based on hours worked at home each month.404 words Making Tax Digital for Income Tax: what sole traders need to knowMaking Tax Digital (MTD) for Income Tax means keeping digital records and sending HMRC quarterly updates with compatible software. It started on 6 April 2026 for the highest earners and widens in 2027 and 2028.335 words How to register for Self Assessment as a new sole traderIf you've started working for yourself, you need to register for Self Assessment by 5 October after the end of the tax year you started. Here's who must register, what you need, and what to do if you've missed it.421 words How to find your UTR numberYour Unique Taxpayer Reference (UTR) is the 10-digit number HMRC uses for your Self Assessment. You need it to file, pay, set up a payment plan and register for CIS. Here's where to find it.346 words How to pay your Self Assessment tax bill, and how long each way takesThe 2025/26 bill is due by 31 January 2027, and HMRC must receive the money by then. Here are the ways to pay, how long each takes, and how to spread the cost.403 words Can't pay your tax bill? How a Self Assessment payment plan worksIf you can't pay your Self Assessment bill in full by 31 January, HMRC may let you pay monthly. For bills up to £30,000 you can usually set it up online without phoning anyone.396 words How to amend a Self Assessment tax returnForgot a CIS statement, missed an expense or used provisional figures? You can correct a filed return. Here's the time limit, how to do it online, and what happens to your bill.340 words Class 2 and Class 4 National Insurance for the self-employed (2025/26)Self-employed people pay National Insurance through Self Assessment. Class 2 changed in 2024 and most people no longer pay it, while Class 4 is a percentage of profit. Here are the 2025/26 figures from GOV.UK.346 words Student loan repayments when you're self-employedWhen you're self-employed, nobody takes student loan repayments from your pay. They're worked out on your tax return and added to your January bill. Here's how it works for 2025/26.368 words How to appeal a Self Assessment late penaltyIf you got a penalty for filing or paying late but something genuinely stopped you, you can appeal. Here's the time limit and what GOV.UK says counts as a reasonable excuse.372 words Self Assessment records checklist for sole traders and subbiesMost tax return stress comes from hunting for paperwork. Work through this checklist for 6 April 2025 to 5 April 2026 and you'll have everything for the 31 January 2027 deadline.399 words Missed the Self Assessment deadline? What to do, step by stepIf you've missed 31 January, don't panic, but don't wait. Penalties and interest grow over time, so the quicker you act, the less it costs.400 words

Dates and bills

CIS, expenses and records

Getting started and what's changing

Paying, penalties and putting things right

Calculators and your tax year

Use the January tax bill calculator for last year's bill, the self-employed tax calculator for this year, and the CIS refund calculator for CIS. BillMyWeek Pro's tax year summary (also in the 14-day free trial, then £1.99/month or £19.99/year) totals your invoices and CIS by UK tax year and exports to PDF or Excel.

Questions

When is the 2025/26 Self Assessment deadline?

11:59pm on 31 January 2027 for online returns and payment.

Why is my January bill so big?

It usually includes the first payment on account for the next year, which is half of last year's bill.

Are these guides tax advice?

No. They're general information checked against GOV.UK. For your own situation, speak to HMRC or an accountant.