Side Hustle + Day Job Tax Calculator

See exactly where every pound of your side hustle lands — and what Self Assessment will add to PAYE.

Estimates only – not tax advice. For planning purposes only; does not replace professional advice or official HMRC calculations. Full disclaimer

Guidance, not advice. This calculator runs the rules as published, it doesn't assess your circumstances. Your actual tax may be affected by factors it doesn't cover (allowances used elsewhere, reliefs, marriage allowance, scheme-specific adjustments). Always seek financial or tax advice from your accountant, or contact HMRC. Read our editorial scope →

Band stacking — where each pound lands

Salary fills bands first through PAYE; the side hustle then lands in whatever band is left.

Why band stacking hurts

Your salary uses bands first through PAYE. Side-hustle profit then stacks on top in whatever band is left. The marginal rate you pay on side-hustle profit depends entirely on where your salary leaves you.

Class 4 NI applies to self-employed profit at 6% between £12,570–£50,270 and 2% above — a separate threshold from your Class 1 NI on salary.

Student loan uses your TOTAL income, so PAYE only collects what the salary triggers — the rest comes out via Self Assessment.

HICBC claws back Child Benefit 1% per £200 above £60,000 adjusted net income, fully gone at £80,000.

Payments on account: if your SA bill is over £1,000 and PAYE collected less than 80%, you pay the balance PLUS 50% of next year as a January POA, then another 50% in July.

Full deep-dive in our side hustle + job guide and real tax rate guide.