Last updated: 27 October 2026

By Stiv · Design, technology and personal finance

Tax / Self AssessmentThe complete collection

Self Assessment guides: every article in one place

These are all my Self Assessment guides in one place, grouped by what you need to know. Start with the deadlines if January is getting close. Then move on to filing fast, the tools that do the work for you, and the jobs to do before the tax year ends on 5 April.

Affiliate disclosure: This page contains affiliate and referral links, which are paid links. If you click one and buy or sign up, I earn a commission or referral bonus at no extra cost to you. Brands don't choose what I feature or what I say about them.

Nothing here is tax or financial advice. Your own position depends on your income and circumstances, so check GOV.UK or speak to a qualified accountant before you rely on any figure.

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Start here

The Self Assessment deadlines, and filing in time

First, the dates that matter for the 2025/26 tax year, then how to file quickly if you have left it late.

Self Assessment deadlines Every 2025/26 date, from registering by 5 October to paying by 31 January, plus each late penalty. Last minute tax return How to file fast when the deadline is days away, and what to have ready before you start. End of year tax return What a Self Assessment return is, who has to file one, and why filing early is the better plan.

The tools

Apps and accountants that file it for you

Next, the services that take the form off your hands, and how they compare on price and support.

Taxfix review UK How Taxfix works, what it costs, and who it suits for Self Assessment. Taxfix vs GoSimpleTax An accountant who files for you against software you fill in yourself, compared on pricing, features and support. Taxfix discount code Up to 35% off a UK accountant filing your return, with the plan prices and how to claim it.

Before 5 April

Jobs to do before the tax year ends

Finally, the moves that can lower next year's bill, which all have to happen before the tax year closes.

Tax year end checklist Seven steps before 5 April, from ISAs and pensions to capital gains and dividends. ISA allowance deadline Why the allowance resets at midnight on 5 April, and what to do before it goes. Dividend tax rise The two-point rise in dividend tax rates from April 2026, who pays more and how an ISA shields dividends.

Self Assessment for 2025/26 at a glance

These are the dates and penalties on GOV.UK's Self Assessment deadlines page and its penalties page, as I read them on 27 October 2026.

What	Deadline
Tell HMRC you need to file (new filers)	5 October 2026
Paper return	11:59pm, 31 October 2026
Online return, if you want the tax collected through your tax code	30 December 2026
Online return	11:59pm, 31 January 2027
Pay what you owe	11:59pm, 31 January 2027
Second payment on account	31 July 2027

Miss the filing deadline and HMRC charges an initial £100 penalty, even if you owe no tax. After three months, daily penalties of £10 start, up to £900. Then, at six months and again at twelve, a further 5% of the tax due or £300 is added, whichever is greater. Paying late adds 5% of the unpaid tax at 30 days, six months and twelve months, plus interest.

How I cover Self Assessment

Each of these Self Assessment guides checks its dates and figures against GOV.UK and HMRC on the day it is written, and I update them when HMRC moves a date or the Budget changes a rate. Where a page recommends a tool, it says what that tool costs and what it does not do. Every Self Assessment guide also links back here, so you can find the rest of the subject from any one of them.

Self Assessment guides: your questions

When is the Self Assessment deadline?

For the 2025/26 tax year, online returns and payment are due by 11:59pm on 31 January 2027. Paper returns are due earlier, by 31 October 2026. My Self Assessment deadlines guide lists every other date.

What happens if I miss the deadline?

HMRC charges £100 straight away, then more the longer the return is late. If you are close to the deadline, my last minute tax return guide covers filing quickly.

Can someone file my tax return for me?

Yes. An accountant can file it for you, and services such as Taxfix match you with one for a fixed fee. My Taxfix review and the Taxfix vs GoSimpleTax comparison cover the options.

Do I need to file a Self Assessment return?

You do if you were self-employed as a sole trader and earned more than £1,000 in the tax year, before expenses. Partners in a business partnership and people who owe Capital Gains Tax have to file too. GOV.UK has a checker for who needs to send a tax return.

Tax rules, deadlines and penalties can change, and your own position depends on your circumstances. This is not tax or financial advice; consider a qualified accountant. This page contains affiliate and referral links, which are paid links. If you click one and buy or sign up, I earn a commission or referral bonus at no extra cost to you. Brands don't choose what I feature or what I say about them.