The system HMRC uses to collect Income Tax from individuals who aren't taxed at source, including sole traders, freelancers, landlords, and company directors. Returns are filed annually or via Making Tax Digital.
Self Assessment is the annual tax filing requirement for anyone running their own business or with untaxed income. It's the form HMRC uses to work out how much Income Tax you owe, and the deadline is fixed - 31 January after each tax year ends. Miss it and penalties start immediately.
For sole traders and freelancers, Self Assessment is the single biggest compliance task each year. You need to pull together all your income and expenses, prove you've calculated profit correctly, and submit to HMRC. Getting this wrong - either overstating profit or understating it - attracts HMRC attention and potential penalties.
For accountants and bookkeepers, Self Assessment has changed. Making Tax Digital now allows businesses to file direct to HMRC via API, rather than using the traditional manual form. This means the onus to file is now on the business (or the software they use), not on the accountant - a significant shift in responsibility.
For business planning, Self Assessment forces discipline. You know the deadline. You know how much profit you need to declare. This focuses minds on record-keeping throughout the year rather than scrambling in January.
Self Assessment is the annual filing and payment cycle for UK self-employed individuals and partnerships.
Key dates:
The calculation:
Start with your tax year profit (6 April to 5 April):
Real example:
A freelance designer in the 2025/2026 tax year (6 April 2025 - 5 April 2026):
Payment is due 31 January 2027.
Making Tax Digital filing:
Instead of manually filling out a form, businesses can now use Making Tax Digital software (like Aarvo) to submit directly to HMRC. You connect your bank feeds, categorise transactions, and Aarvo calculates your profit. You then file the return electronically to HMRC.
Record-keeping is essential:
HMRC requires you to keep records of all income and expenses for at least 5 years. Invoices, receipts, bank statements, mileage logs - keep copies. If HMRC investigates and you can't prove your figures, you lose the benefit of the doubt and may face penalties.
Revenue vs. profit:
Sole traders sometimes confuse income with profit. If you invoice £100,000 but spend £30,000 on expenses, you declare £70,000 profit, not £100,000 income. Get this wrong and you'll overpay tax.
Allowable expenses are specific:
Rent, supplies, professional fees - these are allowable and reduce your taxable profit. Personal expenses, clothes, entertaining (mostly), fines - these are not. Many items fall in the grey area (is working from home rent allowable? yes, but only the business proportion). Your accountant will advise.
National Insurance on top of Income Tax:
Self-employed people pay Class 2 National Insurance (fixed at £163.80 in 2025/2026) and Class 4 (9% on profit between roughly £12,000 and £50,270, then 2% above that). This is on top of Income Tax, so total tax and NI bills can be substantial.
Estimated tax payments:
If you expect to owe more than £1,000 in tax, HMRC may ask you to pay "payments on account" - half your previous year's tax bill, due in January and July, to avoid a large bill at year-end. These are adjustments when you actually file and pay the balance.
Aarvo supports Making Tax Digital for Self Assessment. Connect your bank feeds, and we pull transactions automatically. Categorise income and expenses (or we can auto-categorise), and Aarvo calculates your profit for the tax year.
When you're ready to file, Aarvo submits your return directly to HMRC via the Making Tax Digital API. No accountant needed for the filing step - no manual forms, no transcription errors. Your return is filed electronically and HMRC acknowledges it immediately.
Aarvo also tracks your estimated tax bill throughout the year, so you always know what you might owe by 31 January. If you need to save for tax, you can set aside the estimate and Aarvo will remind you when payment is due.
Sign up free at aarvo.com/signup and Aarvo handles your Self Assessment filing automatically via Making Tax Digital - you just verify and submit.
Self Assessment is HMRC's system for collecting Income Tax from individuals who aren't taxed at source. If you're a sole trader with annual income of £50,000 and the tax office hasn't deducted tax from that income, you file a Self Assessment return showing your profit and the tax you owe - typically due 31 January after the tax year ends.
Sole traders, freelancers, landlords with rental income, company directors who also have other income, and anyone with untaxed income. You're legally required to notify HMRC within 3 months if you're self-employed, and to file a return if your income is above the threshold (currently £1,000) from self-employment or other untaxed sources.
The deadline is 31 January after the tax year ends. The tax year runs 6 April to 5 April. So for the 2025/2026 tax year (6 April 2025 - 5 April 2026), you file by 31 January 2027. Tax is due on the same date. If you file late, penalties apply - 5% of the tax owed, rising to 10% if more than 12 months late.
Start with your revenue for the tax year (6 April to 5 April). Deduct all allowable business expenses - rent, supplies, salary to employees, professional fees, subscriptions, mileage, interest on business loans. The result is profit, which is your taxable income. You pay Income Tax on this profit at the standard rate (20%) or higher rate (40%) depending on your income.
Yes. Aarvo supports Making Tax Digital for Self Assessment. Connect your bank feeds and invoicing data, and Aarvo pulls your profit automatically. You can then file your Self Assessment return directly to HMRC via our platform, so you don't need a separate accountant for this step. Aarvo handles the MTD connection and submission.
Self Assessment is the income tax return you file as an individual. VAT is a separate sales tax you charge to customers (at 20% standard rate) and pay quarterly or monthly to HMRC. You can file both through Aarvo if your income is above the VAT registration threshold (£90,000 in the current year).
Value Added Tax - a consumption tax charged on most goods and services in the UK at a standard rate of 20%. Businesses with turnover above £90,000 must register for VAT, file quarterly returns, and remit tax collected to HMRC.
A tax on the profits of UK limited companies. The current main rate is 25% for profits over £250,000, with a smaller rate of 19% for profits under £50,000. Unlike VAT and Self Assessment, Corporation Tax returns are not yet part of HMRC's Making Tax Digital system.
The total income your business earns from selling products or services, before any costs are deducted. It's the top line of your income statement and the starting point for calculating profit.