National Insurance is the second biggest deduction on most payslips and easily the least understood. It looks like a second income tax, and in most respects it behaves like one, but it runs on different rules and it buys you specific things that income tax does not. Knowing those rules is what lets you tell whether the number on your payslip is right, and whether you are actually on course for a full State Pension.
What You Pay in 2026/27
If you are an employee on the standard category letter, Class 1 National Insurance works like this:
| Annual earnings | Weekly | Monthly | Employee rate |
|---|---|---|---|
| Up to £12,570 (primary threshold) | Up to £242 | Up to £1,048 | 0% |
| £12,571 to £50,270 (upper earnings limit) | £242 to £967 | £1,048 to £4,189 | 8% |
| Over £50,270 | Over £967 | Over £4,189 | 2% |
Take a £35,000 salary. Only the slice above £12,570 attracts NI, so £22,430 is charged at 8%, giving £1,794.40 a year, or about £149.53 a month.
Now take £70,000. The first band runs from £12,570 to £50,270, so £37,700 at 8% is £3,016. The remaining £19,730 sits above the upper earnings limit and is charged at 2%, adding £394.60. Total NI: £3,410.60. Notice what happens at £50,270: your marginal NI rate drops from 8% to 2% at exactly the point your marginal income tax rate jumps from 20% to 40%. That is not an accident, and it is why the combined marginal rate is flatter than most people expect. Our article on what a pay rise really does to your take-home pay works through that in more detail.
NI is not cumulative, and that changes everything
Income tax in the UK is calculated cumulatively across the year, so a big month and a quiet month even themselves out. National Insurance does not work that way. Each pay period is assessed entirely on its own, against that period's thresholds, and nothing is looked at again afterwards.
That has a real consequence for bonuses. Suppose you are on £42,000, paid monthly, so £3,500 a month. In a normal month your NI is (£3,500 minus £1,048) at 8%, which is £196.16.
Now add a £10,000 bonus in one month, taking that month's pay to £13,500. The 8% band is used up first: (£4,189 minus £1,048) at 8% is £251.28. Everything above £4,189, which is £9,311, is charged at 2%, adding £186.22. That month's NI is £437.50, and eleven ordinary months at £196.16 come to £2,157.76. Your NI for the year: £2,595.26.
Had the same £10,000 been paid as an extra £833.33 every month instead, each month's pay would be £4,333.33. That is above the upper earnings limit, so each month you would pay £251.28 plus 2% of £144.33, which is £254.17. Over twelve months that is £3,050.04.
The lump sum saves roughly £455 in National Insurance, purely because the 2% band gets used in one hit rather than being wasted twelve times over. Income tax is identical either way, because it is cumulative. This is one of the few genuinely useful quirks of the system, and it also explains why an unexpectedly large NI deduction in a bonus month is usually correct rather than an error.
Category Letters
Your payslip shows an NI category letter, and it decides which rates apply. Most people are on A. The ones you are most likely to encounter:
- A: the standard letter for most employees.
- C: you have reached State Pension age. You pay no employee NI at all, though your employer still pays its share.
- M: under 21.
- H: apprentice under 25.
- V: a veteran in their first civilian job after leaving the armed forces.
- J or Z: you have deferred NI because you are paying it in another job as well.
- B: a married woman or widow holding a reduced rate election certificate. These are historic and now very rare.
There are further letters for freeports and investment zones. The one worth checking yourself is M. If you turned 21 and nobody updated your record, the letter should change, and while M and A charge employees the same rate, an out of date letter is a sign that your payroll record has not been reviewed.
What National Insurance actually buys
NI is a contributory system, which is the difference between it and income tax. Paying it builds entitlement to a defined list of things. For Class 1 employees, GOV.UK lists the new State Pension, the basic and additional State Pension for older records, New Style Jobseeker's Allowance, contribution-based Employment and Support Allowance, Maternity Allowance and Bereavement Support Payment.
What it does not buy, despite the persistent belief, is the NHS. The health service is funded overwhelmingly from general taxation. Nor does it buy Universal Credit, which is means tested and does not depend on your contribution record at all.
Qualifying years and the state pension
The full new State Pension is £241.30 a week in 2026/27. If your National Insurance record started after April 2016 you need 35 qualifying years to get the full rate, and usually at least 10 qualifying years to get anything at all. People who were contracted out before 2016 often need more than 35.
Here is the part that catches people out. A qualifying year is not the same as a year in which you paid National Insurance. You get a qualifying year if your earnings reach the lower earnings limit, which is £6,708 in 2026/27, even though you pay nothing until £12,570. So someone earning £10,000 a year pays no NI whatsoever and still banks a qualifying year.
You can also get credits without earning at all: while claiming Child Benefit for a child under 12, while on Statutory Maternity Pay, while receiving Carer's Allowance, and in several other situations. If you or a partner stopped claiming Child Benefit because of the High Income Child Benefit Charge, check that you registered for the credits anyway. That mistake has cost people whole qualifying years.
Checking your record and filling gaps
Your National Insurance record and your State Pension forecast are both in your Personal Tax Account on GOV.UK, and they take about two minutes to look at. Do it once, then again every few years.
If you have gaps, you can usually pay voluntary contributions to fill them, normally going back six tax years. Class 3 voluntary contributions cost £18.40 a week in 2026/27, which is £956.80 for a full year.
Do not pay before checking, though. Extra years do not always increase your pension. If you are already on track for the full amount, or if the gap falls in a period covered by the pre-2016 starting amount rules, the money buys you nothing back. The Future Pension Centre exists precisely to answer that question, and calling them first is free.
Where NI goes wrong on a payslip
Three things account for most genuine NI errors. The first is an out of date category letter, most often someone over State Pension age still being charged: if that is you, tell payroll, because they can put it right and refund you. The second is two jobs that each sit below the primary threshold, so neither deducts NI. That is entirely legal, but if each job also sits below the lower earnings limit, neither one gives you a qualifying year, and the earnings are not added together for that purpose. The third is directors, who are assessed on an annual earnings period rather than per pay run, which makes their deductions look wildly uneven month to month and perfectly correct by April.
If your NI looks wrong, run your figures through the net pay calculator first and compare. If the totals still do not reconcile, payroll is the first call and HMRC on 0300 200 3300 is the second.
This page is general information about how National Insurance is calculated, not tax advice, and the figures are for the 2026/27 tax year. HMRC publishes the current rates on GOV.UK, and anything involving your specific contribution record is worth confirming with them directly. The one job genuinely worth putting in the diary is a five minute look at your State Pension forecast, because gaps are cheap to fix within six years and impossible after that.