01 / THE CALCULATOR

Start with your numbers.

Example figures are pre-filled. Replace them with yours.

Your income & costs

2025 / 26
Total business income before costs
£
Excluding mileage entered below
£
Optional · car or van
miles
e.g. salary, before tax
£
Estimated tax bill:
£5,379.40
For the 2025/26 tax year · before any payments on account
How we got thereActual expenses used
Turnover£42,000
Business expenses entered£8,200
Mileage allowance£540
Expenses / allowance used−£8,740
Taxable profit£33,260
Personal allowance used£12,570
Extra Income Tax£4,138
Class 4 National Insurance£1,241.40
Total tax & NI£5,379.40
First payment on account£2,689.70
Total due 31 Jan 2027£8,069.10
Effective rate on profit16.2%

You'll likely also pay 50% of this bill as a first payment on account by 31 Jan 2027, and another 50% by 31 Jul 2027. The January total above includes the first payment.

SET ASIDE EACH MONTH · 4.1 MONTHS TO DEADLINE£1,946.89 / month

This is an estimate for England, Wales and Northern Ireland, not a final HMRC calculation. Other income, reliefs and your individual circumstances can change what you owe.

What about Class 2 NI?

Class 2 is no longer charged from 2024/25. If your profits are £6,845 or more, contributions are generally treated as paid for benefit purposes.

What’s included?

2025/26 Income Tax bands, Class 4 National Insurance, your personal allowance and simplified car or van mileage.

What about January?

The total due includes an indicative first payment on account where applicable. Your HMRC statement may differ.

02 / STAY AHEAD

The calculator for today. The system for all year.

Clear numbers now are good. Keeping them organised as you go is even better.

THE NEXT STEP

Make next January a little easier.

Want this worked out automatically all year? Get the UK Self Assessment Workbook (Excel & Google Sheets) — income, expenses & mileage logs, this same calculator, MTD check and deadlines. £6.99 instant download

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03 / THE USEFUL BITS

Good questions. Clear answers.

The practical things worth knowing before you file. Always check the latest HMRC guidance for your own circumstances.

Do I need to register for Self Assessment?
If your gross trading income is more than £1,000 in a tax year, you generally need to tell HMRC and register for Self Assessment. The registration deadline is 5 October after the end of that tax year. For 2025/26, that means 5 October 2026.
When is the deadline?
The deadline to file your online 2025/26 Self Assessment tax return and pay the balancing amount due is 31 January 2027. The paper return deadline is 31 October 2026. The 2025/26 tax year runs from 6 April 2025 to 5 April 2026.
What are payments on account?
Payments on account are advance payments towards your next tax bill. They usually apply when your Self Assessment bill is more than £1,000 and less than 80% of the tax you owe was collected outside Self Assessment. Each payment is normally half of the previous year’s Income Tax and Class 4 National Insurance bill, due on 31 January and 31 July. This calculator shows an indicative first payment due with your bill on 31 January 2027; HMRC may calculate yours differently.
What is the £1,000 trading allowance?
The trading allowance lets eligible people deduct up to £1,000 from gross trading income instead of claiming actual business expenses. You cannot use both for the same trade. Leave the box unticked and this calculator selects the larger deduction; tick it to model the trading allowance specifically. If your trading income is £1,000 or less, you may not need to report it, but exceptions apply.
Can I claim mileage?
You may be able to use HMRC’s simplified mileage rates for business journeys: 45p per mile for the first 10,000 car or van miles in a tax year, then 25p; 24p per motorcycle mile; or 20p per bicycle mile. Keep a record of dates, destinations, purpose and distance. You cannot generally claim fuel and running costs for the same vehicle alongside simplified mileage costs.
What is Making Tax Digital and does it apply to me?
Making Tax Digital for Income Tax is being phased in based on qualifying income, generally total gross income from self-employment and property. It applies from 6 April 2026 if qualifying income is over £50,000, from 6 April 2027 if it is over £30,000, and from 6 April 2028 if it is over £20,000. Check your position with HMRC; this calculator does not determine your MTD obligations.