Self-Assessment Income Tax & NI Calculator
Self-assessment income tax & NI calculator
For sole traders, landlords and side-hustlers filing a self-assessment return. Estimates your Income Tax, Class 2 and Class 4 National Insurance for 2026/27 — including PAYE income, rental and dividends in the same calc.
Estimate your SA bill
2026/27: PA £12,570 (taper above £100k); basic 20%, higher 40%, additional 45%. Class 2 NIC voluntary (no charge if profit ≥ £6,725); Class 4 NIC 6%/2%. Dividend allowance £500; rates 8.75%/33.75%/39.35%. England/NI/Wales rates.
How self-assessment tax is calculated
Self-assessment combines all your income sources into a single tax bill. The order matters: non-savings income (employment, self-employment, rent) uses the Personal Allowance and bands first, then dividends are added on top using whatever band you are in.
- Personal Allowance — £12,570 of total income free of income tax. Lost £1 for every £2 over £100,000.
- Income Tax — 20% / 40% / 45% bands.
- Class 2 NIC — for self-employed only. Since April 2024, no longer mandatory: profits ≥ £6,725 give you the qualifying year automatically with no payment. Below that, you can pay voluntarily (£3.50/week in 2026/27) to protect your state pension.
- Class 4 NIC — 6% on self-employment profits between £12,570 and £50,270; 2% above. (Cut from 9%/2% in April 2024.)
- Dividend tax — first £500 free; then 8.75% (basic), 33.75% (higher), 39.35% (additional) depending on which band the dividend lands in.
- PAYE credit — any tax already deducted under PAYE is credited against the SA bill. So you only pay (or are refunded) the difference.
Two payments on account in January and July of the following year then reset the cycle for next year.
Frequently asked questions
I have a PAYE job AND self-employment. How does that work?
Both incomes go on the same SA return. The PAYE tax already deducted is credited; the SA calculation works out the total bill across all your income, and you pay the difference (or claim a refund). If your self-employment is small, you might end up with a refund because of the personal allowance and basic-rate band.
Do I have to pay Class 2 NIC?
Not anymore. From April 2024, Class 2 became voluntary. If your self-employment profit is at least £6,725 you automatically get the National Insurance qualifying year credit without paying anything. Below £6,725 you can still pay voluntarily to fill in any gaps in your record.
What expenses can I deduct from rental income?
Letting agent fees, repairs and maintenance (not improvements), insurance, council tax (if you pay), legal and professional fees, ground rent, service charges, and 20% basic-rate tax credit on mortgage interest. Capital improvements add to the base cost when you eventually sell.
What about payments on account?
If your bill is over £1,000, HMRC asks for two “payments on account” — half on 31 January, half on 31 July — based on your previous year’s bill. The actual difference is settled when you file the next return. The calculator shows the headline figure; we always run the payments on account separately when we prepare the return.
I have foreign income — does this calculator help?
It does not include foreign income complications (dual taxation, remittance basis, foreign tax credits). If you have meaningful overseas income, the proper return needs careful handling — book a call and we will price it.
Want this filed properly?
The calculator estimates the bill. We prepare and file SA returns for hundreds of clients each year — fixed fee, all your income sources combined, deadlines tracked.