Parameters in use — tax year 2026–27
| Item | Value | Source |
|---|---|---|
| Personal allowance | £12,570; reduced £1 per £2 over £100,000; zero at £125,140 | GOV.UK, Income Tax rates and allowances |
| England/Wales/NI bands | 20% to £37,700 taxable · 40% to additional threshold · 45% over £125,140 total income | GOV.UK |
| Scotland bands (total income) | 19% to £16,537 · 20% to £29,526 · 21% to £43,662 · 42% to £75,000 · 45% to £125,140 · 48% above | Scottish Budget 2026–27; mygov.scot |
| National Insurance (Class 1) | 8% between £12,570 and £50,270; 2% above | GOV.UK, Employer rates & thresholds 2026–27 |
| Student loans | Plan 1 £26,900 · Plan 2 £29,385 · Plan 4 £33,795 · Plan 5 £25,000 (all 9%) · Postgraduate £21,000 (6%) | GOV.UK, Student loan employer guidance |
| Auto-enrolment pension | Qualifying earnings £6,240–£50,270; total 8% (you 4% net + 1% relief, employer 3%); trigger £10,000 | GOV.UK / DWP review |
| National Living Wage | £12.71 (21+) from 1 April 2026 | GOV.UK; Low Pay Commission |
Traps we check every year
Scotland's two presentations: gov.scot publishes bands by total income; GOV.UK's employer tables publish them net of the personal allowance (the starter band shows as £3,967). Mixing the two breaks calculators — ours uses one consistent basis. Stale thresholds: this year the Scottish starter/basic thresholds rose 7.4% and every student loan threshold except Plan 5 and Postgraduate moved; pages still showing Plan 2 at £28,470 are a year out of date. Pension basis: minimum contributions apply to the qualifying-earnings band, not your whole salary, and the employee's “5%” leaves your pay as 4% under relief-at-source — we model exactly that and say so.
Method
Income tax is computed on annual income after the (possibly tapered) personal allowance, using the England/Wales/NI bands or the six Scottish bands. National Insurance is annualised from the Class 1 thresholds. Pension deductions use the relief-at-source presentation; net-pay-arrangement and salary-sacrifice schemes produce slightly different payslips. Per-period figures divide annual results evenly.
Update log — 1 November 2026: all 2026–27 parameters verified line by line against official pages.