Everything you need to know about Self Assessment tax returns

Self Assessment tax return deadlines

To avoid getting hit with a penalty fee, HMRC must receive your tax return and any money you owe by the deadline.

You can file your Self Assessment tax return any time on or after 6 April, following the end of the tax year it applies to. The sooner you file, the sooner you'll know what you owe – and the more time you'll have to plan for payment.

Along with the 5 October deadline for registering for Self Assessment, HMRC has set the following deadlines:

If you’re a PAYE employee, you can pay your Self Assessment bill through your PAYE tax code if the following apply:

• You owe less than £3,000 (part payments do not count)

• You already pay tax through PAYE (eg, you’re employed or get a company pension)

• You submitted your paper tax return by 31 October or your online tax return online by 30 December

If you’re a trustee of a registered pension scheme or a non-resident company, tax returns must be completed using paper forms and submitted by 31 January after the end of the tax year.

If you’re in a business partnership where your partner is a limited company and they have an accounting date between 1 February and 5 April, paper returns must be submitted 9 months after the accounting date and online returns 12 months after the accounting date.

Self Assessment penalties

If you file your tax return up to 3 months late, you’ll be hit with a penalty of £100. You’ll have to pay more if it’s even later, or if you’re late paying the tax you owe. Interest will also be charged on late payments.

You can estimate the cost of a penalty on the HMRC website.

If you’ve got a genuine reason for submitting a return late, contact HMRC as soon as possible. If you have missed your Self Assessment payment date you can phone the Self Assessment Payment Helpline on 0300 200 3822.

Find out more about Self Assessment penalties in our guide.

What information will I need to complete a Self Assessment tax return?

Before you sit down to complete your tax return, make sure you have everything you need on hand:

• Your 10-digit UTR

• Your National Insurance Number

• Details of your self-employment income

• Details of any self-employment business expenses

• Details of any pension or charitable contributions that may be eligible for tax relief

• Details of property rental income

If you earn an income through employment, you’ll also need:

• A P60 from your employer showing your income and the tax you have already paid

• A P9D or P11D showing any benefits or expenses you received

• A P45 if you have left a job during the tax year

How to complete your Self Assessment tax return

As long as you have the above information ready, filling in the tax return online should be no more daunting than completing any regular expense form. 

The tax return has a main section (SA100) and supplementary sections for income from other sources that you haven’t paid tax on.

Once you’ve entered all of the information, hit “Submit” and you’re all done. HMRC will then calculate if you owe tax, how much tax and what National Insurance contributions you’ll need to pay.

1. The main section (SA100)

The SA100 section covers income from sources other than employment or self-employment, along with any pension or charitable contributions you’ve made. This includes:

• Interest and dividends. Details of taxed and untaxed interest from UK banks and building societies, dividends from UK companies, plus foreign interest and dividends.

• Pension, annuities and state benefits. Details on the total and gross amounts of any State Pension, the gross amount of any other pension lump sums or annuities and details on any benefits, including Jobseeker’s Allowance, Incapacity benefit, Carer’s Allowance, Industrial Death Benefit and Bereavement Allowance.

• Blind Person’s Allowance. You must note whether or not you’re claiming this.

• Student loan repayments. You must note whether or not you’re repaying a student loan and details of deductions made by your employer.

• High-income Child Benefit charge. If you earn over £50,000 and receive Child Benefit, you’ll need to complete this section.

• Marriage Allowance. If your income for the tax year was less than the Personal Allowance, you can transfer the remaining allowance to your spouse.

• Pension contributions. Details on all payments made into a registered pension scheme or annuity contract where contributions were made after tax.

• Charitable donations. Details of all Gift Aid donations.

2. Supplementary pages

If you’re self-employed, have income from property or have capital gains to declare, you’ll need to add the necessary supplementary pages.

These forms are split into two sections: income and expenses.

For self-employment (SA103)

• Income: Everything you’ve earned through self-employment during the tax year, before expenses. If you have other incomes from self-employment, you’ll need to enter the one you earn the most from as your main income.

• Expenses: Anything you’ve spent money on for your business in the last tax year. If you earned below £90,000 during the tax year your expenses can be entered as a total sum. If you earned over £90,000 you’ll need to list them individually. You can view the full list of allowable expenses onGOV.UK.

Note: If you’re a sole trader and claim the trading allowance of £1,000, you won’t be able to claim expenses.

For UK property (SA105)

• Income: The total amount you’ve earned from any rental properties, holiday lettings and land leasing (including any premiums earned)

• Expenses: Can be claimed on the costs of owning and maintaining property, unless you claim the trading allowance. You can view the full list of allowable property letting expenses on GOV.UK.

For capital gains (SA108)

• Income: Capital gains tax is charged when you sell, give away, or otherwise dispose of an asset for profit. Assets include things you own such as property, antiques, or cryptoassets.

• Expenses: Can be claimed for allowable costs on buying and improving assets. You can view the full list of allowable expenses in HMRC’s Capital Gains Manual.

According to GOV.UK, to report any Capital Gains Tax over your annual allowance, you’ll need:

• Calculations for each capital gain or loss you report

• Details of how much you bought and sold the asset for

• The dates when you took ownership and disposed of the asset

• Any other relevant details, such as the costs of disposing of the asset and any tax reliefs you’re entitled to

You must report any Capital Gains Tax on a UK property within 60 days of selling it if you completed the sale after 27 October 2021.

Paying your Self Assessment tax bill

After filing, it can take up to 72 hours after you’ve submitted your return for the final tax calculation to show up in your account.

If you’re applying for a mortgage, you can request your SA302 tax calculation as evidence of your earnings over the past four years.

Key deadlines

• 31 January: Deadline to pay your tax bill

• 31 July: Deadline for your second "payment on account" (if applicable)

Ways to pay your tax return

• Bank transfer (such as CHAPS or Faster Payments)

• Debit card or corporate credit card

• Cheque

• Direct Debit

• Paying-in slip from HMRC (if you still get paper statements)

You cannot pay your tax bill by personal credit card.

Payments on account

Payments on account are advance payments towards your tax bill. You’ll need to make two every year (by 31 January and 31 July), each one covering half of your tax bill, unless:

• Your last tax bill was less than £1,000

• You’ve already paid more than 80% of the tax you owe for the previous tax year

Paying your tax bill in advance with a budget payment plan

If you’re up to date with Self Assessment payments, you can set up a Direct Debit Budget Payment Plan from your online account to make regular payments towards your tax bill.

What happens if I can’t afford my tax bill?

If you can’t afford your tax bill, contact HMRC immediately to discuss a Time to Pay arrangement. You may be eligible for:

• An extension on your payment deadline

• An instalment plan to spread the cost

What is Making Tax Digital for Income Tax?

Making Tax Digital (MTD) for Income Tax is one of the biggest changes to the UK tax system in decades. Starting 6 April 2026, it replaced the traditional annual Self Assessment return for sole traders and landlords who meet the income thresholds.

Rather than filing one return in January, you’ll keep digital records throughout the year and send quarterly updates to HMRC using MTD-compatible software. You’ll then submit a final declaration at the end of the tax year to confirm your total income and finalise what you owe.

Who does MTD apply to?

MTD for Income Tax is being phased in based on gross income from self-employment and property combined (before expenses):

• From April 2026: sole traders and landlords with qualifying income over £50,000

• From April 2027: those with qualifying income over £30,000

• From April 2028: those with qualifying income over £20,000

If your income falls below these thresholds, you’ll continue to use Self Assessment as normal for now. Partnerships are not included yet, though the government plans to extend MTD to them in the future, and plans to introduce MTD for corporation tax have been scrapped for now.

What changes under MTD?

Instead of one annual tax return, you’ll need to make five digital submissions per year: four quarterly updates and one final declaration. Here’s how it breaks down:

• Keep digital records of your income and expenses using MTD-compatible software throughout the year.

• Submit quarterly updates to HMRC summarising your income and expenses (the first deadline for 2026/27 is 7 August 2026).

• Submit a final declaration by 31 January, confirming your total income for the year and any other income sources (such as savings interest or employment income). This replaces your Self Assessment tax return. You’ll still pay your tax bill by 31 January.

The good news is that by keeping on top of your records as you go, that January deadline should feel a lot more manageable. No more scrambling for receipts at the last minute.

How to get MTD-ready

The most important step is choosing the right software. You cannot use HMRC’s standard online Self Assessment portal for MTD submissions. You’ll need software that is recognised by HMRC for MTD.

Tide members can use Tide’s free MTD tool to submit their digital income tax returns. You can track your income and expenses, stay on top of your quarterly submissions, and file directly to HMRC, all from one place. If you’re not yet on MTD, Tide Accounting also lets you generate your Self Assessment form, estimate your tax bill, and file to HMRC from the Tide app.

Please note that the free tool does not cover MTD for VAT. Sole traders and landlords who are registered for VAT can sign up to Tide Accounting. 

Wrapping up

Completing your Self Assessment ensures that you’re paying the right amount of tax, based on what you’ve earned, minus the various expenses you’ve accrued from running your business. In some cases, you may even be owed money from HMRC.

Remember to file your tax return as soon as possible. Take your time to gather the relevant information and complete the form step by step. Follow these top tips to help you file your tax return stress-free:

• Consider using HMRC-recognised software. Filing through HMRC-recognised software can streamline the process by auto-populating fields and reducing manual errors. If you’re required to use MTD, you’ll need MTD-compatible software to submit quarterly updates. Tide’s free Making Tax Digital tool lets you file directly to HMRC from your Tide account.

• Download HMRC’s free help sheets to assist you with each section of the tax return.

• Don’t rush it. You don’t need to complete your Self Assessment return in one go. You can save your progress and come back to it.

• Keep accurate records. Around one in 20 tax returns is subject to further investigation. If your return is chosen for investigation, you’ll need to produce records to show that the figures are correct. If you’re self-employed, you must keep records for six years.

• Before you hit submit on your tax return, go back through each section to ensure you’ve completed everything you need to.

• If you’ve made a mistake, you can make changes up to 12 months after the filing deadline for the tax year in question.