Self-Assessment
Self-Assessment is how HMRC works out the income tax you owe on anything that isn't taxed at source — self-employed income, rental income, dividends, capital gains and more. The system is straightforward once you understand it, but the deadlines and penalties bite hard if you don't. These guides walk you through registration, payments, the calculation, and how to fix things when they go wrong.
Guides
Read our Self-Assessment guides
Plain-English walkthroughs of the most common questions clients ask.
- 1
How do I amend or correct information on my Self-Assessment tax return?
Sole traderLandlordContractorCorrecting your Self-Assessment tax return is straightforward if you act within the deadlines, ensuring your tax records with HMRC are accurate.
- 2
How do I report capital gains or property income on my Self-Assessment?
LandlordLimited companySole traderSelling an asset for a profit or earning income from property both need to be reported on your Self-Assessment tax return, and understanding the rules for each is key to accurate reporting.
- 3
What should I do if HMRC opens an investigation or compliance check?
Sole traderLimited companyDirectorReceiving a letter from HMRC about a compliance check or investigation can be unsettling, but understanding the process and knowing how to respond calmly and effectively is key.
- 4
What should I do about HMRC letters, demands, or penalties?
Sole traderLandlordContractorWhen you receive a letter, demand, or penalty notice from HMRC, it's crucial to act promptly and understand its contents to avoid further issues.
- 5
What is MTD for ITSA and what do I need to do?
Sole traderLandlordMaking Tax Digital for Income Tax Self Assessment (MTD for ITSA) is a significant change to how sole traders and landlords report their income and expenses to HMRC, moving from annual tax returns to digital…
- 6
How do I get an SA302 or accountant's reference for my mortgage application?
Sole traderLimited companyLandlordAn SA302, or a combination of your Tax Year Overview and Tax Calculation, is a summary of your income and tax paid, often required by mortgage lenders to assess your affordability as a self-employed individual.
- 7
What is Self-Assessment and what do I need to do?
Sole traderLimited companyContractorSelf-Assessment is HMRC's system for collecting Income Tax from individuals whose income isn't automatically taxed through Pay As You Earn (PAYE), requiring you to declare your income, calculate your tax, and make…
- 8
How do Self-Assessment payments on account work and can they be reduced?
Sole traderContractorLimited companySelf-Assessment payments on account are advance payments towards your next tax bill, designed to spread the cost of your tax liability across the year rather than paying it all at once.
- 9
How do I register for Self-Assessment and get my Unique Taxpayer Reference (UTR)?
Sole traderLimited companyContractorRegistering for Self-Assessment is the essential first step to declaring untaxed income to HMRC and obtaining your Unique Taxpayer Reference (UTR).
- 10
How is my Self-Assessment tax liability calculated and why are the figures what they are?
Sole traderLandlordContractorYour Self-Assessment tax bill is calculated by adding up all your taxable income, subtracting allowances and reliefs, applying the correct tax rates and National Insurance, and then adjusting for any payments on…
- 11
When and how will I receive my Self-Assessment tax refund?
Sole traderLandlordContractorIf you've overpaid tax through Self-Assessment, HMRC will typically refund the money directly to your bank account, or offset it against future tax bills, usually within 2-4 weeks for online returns.
Key facts
The headline figures
31 Jan
Online filing deadline
Following the tax year that ended 5 April
5 Oct
Registration deadline
If new to Self-Assessment
31 Oct
Paper return deadline
Earlier than online — most people file online
£12,570
Personal allowance
Tax-free, 2025/26
Up to £50,270
Basic-rate band
Including allowance, 2025/26
£100
Late-filing penalty
Initial fine — escalates further if unpaid
Annual cycle
Key dates and deadlines
The events you can't afford to miss in a typical year.
- 6 April
Tax year begins
The clock starts. You can file as early as the next day if you have all your figures.
- 5 October
Register by this date (if new)
Tell HMRC you need to complete a Self-Assessment for the tax year just ended.
- 31 October
Paper return deadline
Almost everyone files online instead — but if you must paper-file, this is your cut-off.
- 31 January
Online return + payment deadline
File your return AND pay your tax. Miss it and an automatic £100 penalty kicks in.
- 31 January
First payment on account due
If your bill was over £1,000, you also pay 50% of next year's expected bill on this date.
- 31 July
Second payment on account due
The other 50% of next year's expected bill.
Useful resources
Official tools and references
Sign in to file your Self-Assessment
Government Gateway sign-in for filing your return online.
gov.uk
Register for Self-Assessment
Tell HMRC you need to file — different forms depending on whether you're self-employed, a partner, or filing for another reason.
gov.uk
Check what you owe (your HMRC account)
Your personal tax account shows balances, payment history, and any HMRC messages.
gov.uk
Take-home tax calculator
Estimate the tax on your income before filing.
Clever Accounts
Quick answers
Self-Assessment FAQs
Who needs to file a Self-Assessment?
What if I miss the 31 January deadline?
Can I file early?
What are payments on account?
Do I still need to file if I had no self-employed income?
Need help with self-assessment?
Speak to a qualified accountant
Our team specialises in self-assessment for UK small businesses, contractors and landlords. No obligation, no sales pitch — just a clear answer to your specific situation.