Frequently Asked Questions

HMRC PAYE Tax Table Routines prescribe per-period rounding (weekly / monthly) that doesn't equal a flat division of the annual figure. Switch the calculation basis to Annual (Self Assessment view) for the year-end total or keep monthly / weekly to match the per-payslip number.

Tax codes encode your personal allowance and any special treatment.

• 1257L — standard code, full £12,570 personal allowance.
• K-codes — negative allowance (extra taxable amount, e.g. taxable benefits).
• BR / D0 / D1 — flat-rate codes (basic / higher / additional rate on every penny). Common for second jobs.
• S- prefix — Scottish taxpayer (uses SRIT bands).
• C- prefix — Welsh taxpayer (currently same as rUK numerically).
• 1257M / 1257N — marriage allowance transferred in / out.
• NT — no tax (rare; usually applies to specific reliefs).
• W1 / M1 / X markers — force non-cumulative basis.

Roughly: outside-IR35 contracts → Limited Company is more tax-efficient because you can split income between salary and dividends. Inside-IR35 → an umbrella is simpler than running a Ltd Co you can't optimise. Use the IR35 calculator to see the actual £ delta for your specific day rate.

Yes. Tick the Scotland box, or use a tax code with an S prefix (e.g. S1257L). The calculator uses Scottish income tax bands (SRIT). Note: dividend tax is not devolved — Scottish taxpayers still use rUK bands for dividends, even though their salary uses Scottish bands. Use the dividend tax calculator to see the split.

All three put money in your pension; they differ in when the tax break is given.

• Relief at Source — contribution from net pay; provider adds basic-rate relief; higher-rate via Self Assessment. Common with NEST.
• Net Pay arrangement — contribution from gross before income tax; NI on full gross. Common with occupational schemes.
• Salary Sacrifice — agreed lower salary; both income tax and NI on the reduced figure. Best for take-home; reduces statutory pay base (e.g. SMP).

HMRC's Approved Mileage Allowance Payment (AMAP) rates apply: 45p per mile for the first 10,000 business miles in the tax year, then 25p per mile after that (cars and vans).

Enter your total business miles in the Sole Trader calculator and the allowance is added to your expenses automatically, reducing your taxable trading profit before income tax and Class 4 NI are applied. Source: HMRC AMAP guidance ↗.

It's an estimate. The math follows the HMRC spec to the penny for standard PAYE scenarios, but your actual liability depends on data we don't have (other employments, benefits in kind, capital gains, etc.). Don't file a Self Assessment off this; consult HMRC's guidance or a qualified UK accountant for final figures. See Terms of Use for the full disclaimer.

Yes — public, free, throttled at 60 requests / minute per IP. POST your inputs to /api/calculate/<mode>/ where mode is one of paye, limited_co, umbrella, ir35 or sole_trader. See the API documentation for request shapes and curl examples.

Yes — an embeddable <iframe> widget is live at /business/, free for any domain or volume. The calculation engine is also open source under the AGPL-3.0 licence — fork it or call the public API and build your own UI.