The United Kingdom: personal allowance, bands and National Insurance
Most people receive a personal allowance of £12,570 tax-free. In England, Wales and Northern Ireland, income above it is taxed at 20% up to £50,270 of total income, 40% up to £125,140 and 45% beyond. Scotland sets its own scale of six bands running from 19% to 48%, so the same salary gives a different answer north of the border; National Insurance is identical either way. The allowance is tapered once income passes £100,000, reduced by £1 for every £2 earned, and disappears completely at £125,140. In that range the effective marginal rate is 60% before National Insurance, which is why the calculator flags a reduced allowance.
Employee Class 1 National Insurance is 8% on earnings between £12,570 and £50,270 a year and 2% above that. Unlike income tax it is worked out per pay period rather than cumulatively, but on a steady salary the annual total is the same.
Personal allowance £12,570 → taxable £47,430.
Income tax: 20% on the first £37,700 = £7,540; 40% on the remaining £9,730 = £3,892. Total
£11,432.
National Insurance: 8% on £37,700 (£12,570 to £50,270) = £3,016; 2% on the £9,730 above = £194.60. Total £3,210.60.
Take-home: £60,000 − £11,432 − £3,210.60 = £45,357.40 a year, £3,779.78 a month.