Self-Assessment Tax Calculator UK
Estimate your full tax bill including Class 4 NI and payments on account
Self-Assessment Tax Calculator 2025/26
Enter your income from all sources and your allowable deductions. The calculator estimates your income tax, Class 4 NI, and payments on account for 2025/26.
Who Needs to File a Self-Assessment Tax Return?
You are required to register for and complete a Self-Assessment tax return if any of the following applied to you in the 2025/26 tax year (6 April 2025 to 5 April 2026):
- You were self-employed as a sole trader and earned more than £1,000 gross (before expenses) from your business
- You are a partner in a business partnership
- You are a company director (unless the company is non-profit and you receive no pay or benefits)
- You received income from renting out property (above the £1,000 property allowance)
- You received additional income over £2,500 that was not taxed at source (e.g., savings interest above your Personal Savings Allowance)
- You had total income above £100,000 (personal allowance tapering applies)
- You received Child Benefit and your or your partner's income exceeded £60,000 (High Income Child Benefit Charge)
- You have capital gains from selling shares, property (not your main home) or other assets above the annual exempt amount
- You received income from abroad or were not UK resident for all or part of the year
- You received income from a trust or settlement
- You want to claim certain tax reliefs such as EIS, SEIS, or VCT relief
If you are unsure whether you need to file, HMRC offers an online checker at gov.uk. Registering for Self-Assessment for the first time must be done by 5 October following the end of the relevant tax year. HMRC Self Assessment helpline: 0300 200 3310.
Self-Assessment Key Deadlines 2025/26
Self-Assessment Penalty Table – What You Risk if You Miss Deadlines
| Offence | Penalty |
|---|---|
| Late filing (online) — immediate penalty | £100 (applies even if no tax is owed) |
| Filing more than 3 months late | £10 per day (up to 90 days = £900 maximum) |
| Filing more than 6 months late | Additional 5% of tax owed or £300 (whichever is greater) |
| Filing more than 12 months late | Additional 5% of tax owed or £300 (whichever is greater) |
| Late payment (tax unpaid after 31 Jan) | 5% of unpaid tax after 30 days |
| Late payment — 6 months | Further 5% of unpaid tax |
| Late payment — 12 months | Further 5% of unpaid tax |
| Interest on unpaid tax | Bank of England base rate + 2.5% per annum |
| Inaccurate return (careless) | Up to 30% of extra tax owed |
| Inaccurate return (deliberate) | Up to 70% (or 100% for concealed) |
HMRC may waive penalties in cases of genuine reasonable excuse (e.g., serious illness, death of a close relative). A reasonable excuse must be reported promptly once the excuse is removed. HMRC Self Assessment helpline: 0300 200 3310.
Income Tax Rates for Self-Assessment 2025/26
Self-employed individuals and those with multiple income sources pay income tax under the same rate bands as employed people, calculated on total taxable income from all sources.
| Tax Band | Taxable Income (2025/26) | Rate |
|---|---|---|
| Personal Allowance | Up to £12,570 | 0% |
| Basic Rate | £12,571 – £50,270 | 20% |
| Higher Rate | £50,271 – £125,140 | 40% |
| Additional Rate | Above £125,140 | 45% |
The personal allowance tapers away for incomes above £100,000 — for every £2 of income above £100,000, £1 of personal allowance is lost. This creates an effective 60% marginal rate between £100,000 and £125,140. Pension contributions or Gift Aid donations can restore the personal allowance in this band.
Class 4 National Insurance for the Self-Employed 2025/26
Self-employed people pay Class 4 National Insurance on their business profits through Self-Assessment. Class 4 NI does not give access to additional state benefits — it funds the National Insurance system generally. From April 2024, Class 2 NI was abolished for most self-employed people.
| Profit Level | Class 4 NI Rate 2025/26 |
|---|---|
| Below £12,570 | 0% |
| £12,570 – £50,270 | 6% |
| Above £50,270 | 2% |
Class 4 NI is calculated on profits (income after allowable business expenses) not on turnover. Self-employed people with profits below £6,725 may wish to pay voluntary Class 3 NI (£17.45 per week in 2025/26) to protect their State Pension entitlement if they have gaps in their NI record.
Dividend Tax Rates 2025/26
Company directors and shareholders who receive dividend income must declare it on their Self-Assessment return if it exceeds the £500 dividend allowance. Dividend income is taxed at lower rates than ordinary income:
| Tax Band | Dividend Tax Rate 2025/26 |
|---|---|
| Dividend Allowance | 0% (first £500 of dividends) |
| Basic Rate taxpayer | 8.75% |
| Higher Rate taxpayer | 33.75% |
| Additional Rate taxpayer | 39.35% |
Dividends sit on top of other income when determining your tax band. If you have employment income of £45,000 and dividends of £10,000, the dividends push you into the higher rate band and are taxed accordingly (above the £500 allowance).
Allowable Deductions for Self-Employed People
Self-employed individuals can deduct allowable business expenses from their turnover to calculate taxable profit. HMRC requires expenses to be "wholly and exclusively" for business purposes. Key allowable deductions include:
- Trading allowance (£1,000): Instead of claiming actual expenses, those with gross trading income up to £1,000 pay no tax. Above £1,000, you choose actual expenses or the allowance — whichever is more beneficial.
- Home office expenses: HMRC flat rate is £6/week (no receipts needed) or £26/month. Alternatively, calculate the proportion of home costs (mortgage interest or rent, utilities) attributable to business use based on rooms used and hours worked.
- Professional subscriptions: HMRC maintains a list of approved professional organisations. Membership fees for trade bodies and professional associations are deductible where membership is necessary for the business.
- Pension contributions: Contributions to a personal pension (SIPP or stakeholder pension) made by the self-employed receive tax relief at source at the basic rate, with higher rate relief claimable through Self-Assessment.
- Gift Aid donations: Charitable donations made under Gift Aid extend the basic rate band, effectively giving higher and additional rate taxpayers extra tax relief through Self-Assessment.
- Property allowance (£1,000): Property rental income up to £1,000 is exempt from income tax. Above £1,000, either deduct the allowance or actual allowable letting expenses — whichever gives a better result.
Payment on Account — How It Works
HMRC requires self-employed taxpayers to make advance payments towards the following year's tax bill if the total bill exceeds £1,000 and less than 80% of tax was deducted at source. Each payment on account equals 50% of the previous year's total tax and Class 4 NI bill.
Example: If your total 2025/26 tax bill (income tax + Class 4 NI) is £8,000 and you paid £2,000 in PAYE, the balancing payment is £6,000. HMRC also requires two payments on account for 2026/27 of £4,000 each (50% of the £8,000 total bill). On 31 January 2027, you therefore pay £6,000 (balancing) + £4,000 (first payment on account) = £10,000. A further £4,000 is due on 31 July 2027.
Frequently Asked Questions: Self-Assessment UK 2025/26
Who needs to complete a Self-Assessment tax return in the UK?
You must file if you were self-employed earning over £1,000, a company director, received rental income, had total income above £100,000, received dividends above the allowance, had untaxed savings interest above your Personal Savings Allowance, or received Child Benefit with income over £60,000. HMRC Self Assessment helpline: 0300 200 3310.
What are the key Self-Assessment deadlines for 2025/26?
31 October 2026 (paper return); 31 January 2027 (online return + balancing payment + 1st payment on account); 31 July 2027 (2nd payment on account). Register by 5 October 2026 if filing for the first time. HMRC helpline: 0300 200 3310.
What is payment on account in Self-Assessment?
Payments on account are advance payments towards next year's tax bill, required when your tax bill exceeds £1,000. Each payment is 50% of the previous year's total tax and NI. First payment is due 31 January (with the balancing payment); second is due 31 July. You can apply to reduce them if your income has dropped.
What expenses can I deduct as a self-employed person?
Allowable deductions include office costs, business travel (not commuting), business clothing (uniforms, not ordinary clothes), staff costs, advertising, professional subscriptions, accountancy fees, business insurance, and capital allowances for equipment. The trading allowance of £1,000 can substitute for actual expenses if it gives a better result.
Do I pay Class 4 National Insurance if I am self-employed?
Yes. Class 4 NI is 6% on profits between £12,570 and £50,270, and 2% above £50,270 (2025/26). Class 2 NI was abolished from April 2024. Self-employed people with profits below £6,725 can pay voluntary Class 3 NI (£17.45/week) to protect State Pension entitlement.
What are the penalties for missing the Self-Assessment deadline?
£100 immediately for late filing (even if no tax is owed); £10/day after 3 months (up to £900); 5% surcharge after 6 months; another 5% after 12 months. Late payment incurs 5% surcharges at 30 days, 6 months and 12 months plus daily interest. HMRC Self Assessment helpline: 0300 200 3310.
How does the trading allowance affect my Self-Assessment?
If gross trading income is £1,000 or below, no tax is due and you do not need to register for Self-Assessment. Above £1,000, you can deduct the £1,000 trading allowance instead of actual expenses — useful if your actual expenses are below £1,000. The property allowance (also £1,000) applies separately for rental income.
Written by Mustafa Bilgic (MB) | Last updated: February 2026 | Based on HMRC 2025/26 tax rates and Self-Assessment rules. HMRC Self Assessment helpline: 0300 200 3310. This calculator provides estimates only and does not constitute tax advice. Consult a qualified accountant or tax adviser for your individual circumstances.