Tax return calculator for the January bill
Find out what you will actually pay HMRC on 31 January, including the payment on account most people forget, and what is due again on 31 July. Free, with no sign-up. The tool remembers your last entries in this browser and does not send them anywhere.
- Balancing payment and payments on account
- Applies the £1,000 and 80% rules
- Shows both dates: 31 January and 31 July
Enter the year's turnover and costs, plus any payments on account you already made for that year.
The working
| Income Tax through Self Assessment | £4,386.00 |
|---|---|
| Class 4 National Insurance | £1,315.80 |
| Bill for 2026/27 | £5,701.80 |
| Less payments on account already made | -£0.00 |
| Plus first payment on account for 2027/28 (half the bill) | £2,850.90 |
| Due 31 January 2028 | £8,552.70 |
2026/27 rates for England, Wales and Northern Ireland, from gov.uk. An estimate, not tax advice: it leaves out CIS deductions already taken, student loans, pension relief and Scottish rates.
What you pay on 31 January
On 31 January you usually pay two things at once: whatever is still owed for the tax year that ended the previous April (the balancing payment), and the first payment on account towards the year you are already in. Six months later, on 31 July, the second payment on account is due. The calculator works out all three.
This is how GOV.UK explains the bill. The balancing payment is the year's total tax minus any payments on account you made for it. Each payment on account is usually half of the year's bill. The figure this tool calls the year's bill is Income Tax plus Class 4 National Insurance, less any tax already taken through PAYE.
The tool opens with this example: a self-employed gardener in their first full year, 2026/27, in England, with no other job and no payments on account made yet.
- Profit: £46,000 turnover − £11,500 expenses = £34,500.
- Income Tax: 20% × (£34,500 − £12,570) = 20% × £21,930 = £4,386.00.
- Class 4 National Insurance: 6% × £21,930 = £1,315.80.
- Bill for 2026/27: £5,701.80. Nothing has been paid towards it, so the balancing payment is the full £5,701.80.
- First payment on account for 2027/28: half of £5,701.80 = £2,850.90.
- Due by 31 January 2028: £5,701.80 + £2,850.90 = £8,552.70.
- Due by 31 July 2028: the second payment on account, £2,850.90. That is £11,403.60 inside six months, on a year's bill of £5,701.80.
Payments on account: the rules
Payments on account are advance payments towards next year's bill, based on this year's. HMRC assumes next year will look like this one and collects it in two halves, in January and July, during the year. They are made up of Income Tax and Class 4. HMRC's Self Assessment manual confirms capital gains tax and student loan repayments are left out; those go in the balancing payment.
How much
Each payment is half of the previous year's bill, after taking off tax already deducted at source such as PAYE. A bill of £5,701.80 means two payments of £2,850.90.
When
By midnight on 31 January during the tax year, and by midnight on 31 July just after it ends. For 2027/28, that is 31 January 2028 and 31 July 2028.
Under £1,000: none
If last year's bill, after tax deducted at source, was less than £1,000, no payments on account are due. You pay the bill in one go each January.
Over 80% at source: none
If more than 80% of the year's tax was already paid outside Self Assessment, mostly through PAYE on a job, no payments on account are due either.
The second year, when it evens out
The first January is the expensive one, because you pay a full year's bill and half of the next one together. After that, payments on account you have already made come off the balancing payment, so January only collects the difference plus the next instalment.
Carry the gardener on a year. In 2027/28, profit rises to £40,000 (£52,000 turnover, £12,000 expenses). They have paid £2,850.90 twice towards it, £5,701.80 in all.
- Bill for 2027/28: Income Tax £5,486.00 plus Class 4 £1,645.80 = £7,131.80.
- Balancing payment: £7,131.80 − £5,701.80 = £1,430.00.
- First payment on account for 2028/29: half of £7,131.80 = £3,565.90.
- 31 January 2029: £1,430.00 + £3,565.90 = £4,995.90. 31 July 2029: £3,565.90.
- This example assumes 2026/27 rates and thresholds still apply in 2027/28. The basic rate limit and Personal Allowance are frozen until April 2031, but rates can change at any Budget.
If you have a job as well
A PAYE wage changes the January bill in two ways. The wage pushes the business profit up the bands. And the tax your employer has already sent to HMRC counts towards the 80% test, so plenty of people with small side businesses never get asked for payments on account. Plenty do, though, and the two cases can look almost identical.
The calculator assumes your employer taxed your wage on a standard tax code, and treats that as tax paid at source. Two worked cases, both for 2026/27:
Wage £45,000, side profit £5,500
Total Income Tax £7,632, of which £6,486 came off the wage. The extra due is £1,146. Tax at source is 85% of the total, over 80%, so no payments on account. January bill: £1,146.
Wage £35,000, side profit £7,000
Total Income Tax £5,886, of which £4,486 came off the wage. The extra due is £1,400. Tax at source is about 76%, under 80%, and £1,400 is over £1,000, so payments on account apply: £1,400 + £700 in January, £700 in July.
Which January pays for which year
Self Assessment always runs a year behind. The return due by 31 January 2027 is for 2025/26, the tax year that ended on 5 April 2026. Your 2026/27 profit is not settled until 31 January 2028. The tool is set to 2026/27, so its dates read 31 January 2028 and 31 July 2028. For a 2025/26 return the sums come out the same; just read the dates a year earlier, 31 January 2027 and 31 July 2027.
Outside Scotland, the sums come out the same in both years. GOV.UK's current and past rates table shows the same Personal Allowance (£12,570), 20% band (£37,700) and higher rate limit for 2025/26 and 2026/27. The National Insurance table shows Class 4 at 6% from £12,570 to £50,270 and 2% above in both. Only voluntary Class 2 differs: £3.50 a week and a £6,845 threshold in 2025/26, against £3.65 and £7,105 in 2026/27.
Other deadlines for the 2025/26 return: register by 5 October 2026 if you are new, send a paper return by 31 October 2026, or file online by 31 January 2027. If you owe under £3,000 and already pay tax through PAYE, you can have it collected through your tax code instead, as long as you file online by 30 December 2026.
Planning for the bill before January
The safest plan is to save for the bill as the money comes in, not after the return is done. Take the tool's total for 31 January and 31 July, divide by the months left, and move that amount into a separate account on the day each month's invoices are paid. January is a quiet month for many trades, which is exactly when the biggest payment falls.
- Profit dropping? If you expect next year's bill to be lower, you can ask HMRC to reduce your payments on account, online or with form SA303. Cut them too far and HMRC charges interest on the shortfall.
- CIS subcontractor? Deductions taken from your pay count as advance payments towards your tax and National Insurance, so the January bill is lower than this tool shows. The tool does not subtract them; the CIS calculator shows what has been taken.
- Paying late? Interest runs on anything unpaid, and penalties apply to late returns and late payments.
- Making Tax Digital? If you joined from 6 April 2026, the quarterly updates are summaries, not extra bills. HMRC confirms the 31 January return deadline stays, and you still pay by the usual dates.
What the estimate does not cover
The figures are a guide for budgeting, not tax advice, and it uses the Income Tax bands for England, Wales and Northern Ireland. Scottish taxpayers have their own Income Tax bands, so the figures will be off. It also leaves out student loan repayments and capital gains, which add to the balancing payment, plus pension contributions, rent, savings, dividends and anything HMRC has already credited to your account. Your HMRC online account shows the real figures once your return is in. If the number matters, check it with an accountant before you rely on it.
For how the year's tax itself is worked out, band by band, use the self-employed tax calculator.
Common questions
How is my tax return bill calculated?
Your profit for the tax year is taxed at the Income Tax rates, plus Class 4 National Insurance on the profit. Payments on account you already made for that year come off. Whatever is left is the balancing payment, due by 31 January after the year ends, usually with the first payment on account for the next year.
Why is my first Self Assessment bill so high?
Because the first January normally includes the whole of last year's bill plus a payment on account worth half of it towards this year. A £5,701.80 bill becomes £8,552.70 on 31 January, with another £2,850.90 in July. From the second year, earlier payments on account bring the January figure down.
Do I have to make payments on account?
Only if last year's bill was £1,000 or more and 80% or less of your tax was paid at source, for example through PAYE. If either rule applies, you pay the whole bill once a year by 31 January.
Are payments on account 50% of my tax bill?
Each one is usually half of the previous year's Self Assessment bill, so the two together equal a full year's bill. Both Income Tax and Class 4 go into them, but not student loan repayments or capital gains tax.
Can I reduce my payments on account?
Yes, if you expect lower profit this year. Apply through your HMRC online account or on form SA303. If your actual bill turns out higher than the reduced payments, you pay the difference with interest.
When is the next tax return deadline?
The online return for 2025/26 is due by 11:59pm on 31 January 2027, and so is any tax owed. Paper returns for that year are due by 31 October 2026. The 2026/27 return is due by 31 January 2028.
Does Making Tax Digital change when I pay?
HMRC says quarterly updates are not tax returns and do not replace one, and the return is still due by 31 January. The calculator's payment dates follow the existing Self Assessment rules. In the first year, 2026/27, HMRC is not giving penalty points for late quarterly updates.
Is a tax return calculator the same as a tax refund calculator?
No. Many pages with this name estimate a PAYE refund for employees. This one is for people who file a Self Assessment return because they are self-employed, and it shows what you owe and when.
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