MTD-ready spreadsheet
Self Assessment Tax Estimator 2026/27
Know what you owe HMRC before January, not after.
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Enter your income, expenses, pension and any PAYE salary. The spreadsheet works out your Income Tax, Class 4 National Insurance, your total bill, your effective rate, what to set aside each month, and whether you'll be caught by Payments on Account.
- Built for the 2026/27 tax year (England, Wales & NI rates)
- Handles mixed income — self-employment plus a salary plus property
- Shows the Payments on Account trap before it bites
- A monthly set-aside figure, so the bill is never a shock
- Works in Excel, Google Sheets and Numbers
- Every formula visible and editable — nothing locked, nothing hidden
Made by Fableworks HQ. Designed and built by us using spreadsheet tools with AI assistance, and every calculation is human-checked and unit-tested.
Secure checkout by Paddle · instant download · VAT handled for you · 14-day money-back guarantee
A look inside — worked example
| Your figures | Amount |
|---|---|
| Self-employment income | £48,000 |
| Allowable expenses | −£6,000 |
| Taxable profit | £42,000 |
| Income Tax | £5,886 |
| Class 4 National Insurance | £1,766 |
| Total due to HMRC | £7,652 |
| Set aside each month | £638 |
Illustrative 2026/27 example (England, Wales & NI). Every figure updates the moment you change a cell.
Why buy this when AI is free?
Fair question, and the honest answer is that a chatbot will give you a number. It will not give you something you can check, keep, or open again in March when your figures have moved. This is a file you own: every formula is visible, change one cell and the whole year re-calculates, and you can send it to your accountant exactly as it is.
It is also doing a different job from a calculator — ours included. A calculator answers one question once. This holds the whole year: the monthly set-aside, the Payments on Account trap that catches people in their second year, and a salary or property income sitting alongside self-employment.
And you do not have to take our word for the arithmetic. The tax logic behind our free calculators is covered by 81 unit tests that run before anything ships — the 2026/27 bands, Class 4 National Insurance, Payments on Account and Section 24. Check our maths for free first, then decide whether the £9 version is worth it to you.
Straight answer on the limits: this is an estimate and planning tool, not HMRC-recognised software, and it does not submit anything to HMRC on your behalf. If you need to send quarterly updates, our free list of recognised software shows which products do that, and which are free.
Questions before you buy
What exactly do I get, and how?
One spreadsheet file, downloaded the instant your payment clears (Paddle also emails you a secure link). It opens in Excel, Google Sheets and Numbers. No account, no subscription and nothing to install.
Can I edit it, or is it locked?
Nothing is locked or password-protected. Every formula is visible and editable — change the numbers, add rows, adapt it to your own situation. It's yours to keep.
Which tax year and rates does it use?
It's built for the 2026/27 tax year using the England, Wales & Northern Ireland Income Tax bands and Class 4 National Insurance thresholds, and it flags Payments on Account when they apply.
Is this tax advice?
No. It's an estimate and planning tool, not tax or financial advice. Always confirm your own position with GOV.UK or your accountant.
What if it's not right for me?
There's a 14-day money-back guarantee. If it isn't useful, email us within 14 days for a full refund.
Secure checkout by Paddle · instant download · VAT handled for you · 14-day money-back guarantee