Income Tax, the Personal Allowance, and National Insurance — explained against a real example payslip.
A UK payslip separates Income Tax and National Insurance into two distinct lines — and treating them as one combined “tax” figure is the most common way people misread their own payslip. Here’s how they actually work, using a real example.
The scenario
On a gross salary of £3,500/month (£42,000/year) in England, Wales, or Northern Ireland, here’s the full breakdown this calculator produces:
- Gross Salary
- £3,500/mo£42,000/yr
- PAYE Income Tax
- £491/mo£5,886/yr
- Class 1 National Insurance
- £196/mo£2,354/yr
- Effective Tax Rate
- 19.6%
Employer pays
Total fund contribution
Line by line
Income Tax. Everyone gets a Personal Allowance — currently £12,570 a year — earned entirely tax-free before Income Tax applies at all. Income above that is taxed in bands: 20% (basic rate), 40% (higher rate) above £50,270, and 45% (additional rate) above £125,140. This example uses the England, Wales, and Northern Ireland bands — Scotland sets its own, different rates.
National Insurance. A separate system funding specific state benefits including the State Pension, with its own thresholds: nothing due up to the Primary Threshold (aligned with the £12,570 Personal Allowance), then 8% between that threshold and the Upper Earnings Limit (£50,270), dropping to 2% above that. Because it’s calculated independently of Income Tax — both from gross pay, but separately — it’s shown as its own line rather than folded into one number.
The detail that catches high earners out
The Personal Allowance itself starts shrinking for anyone earning over £100,000 a year — it reduces by £1 for every £2 earned above that threshold, reaching zero entirely at £125,140. This calculator doesn’t model that tapering, so results for gross salaries above roughly £100,000 will understate the real tax owed slightly. It’s a narrow band of earners it affects, but worth knowing if it applies to you.
