National Insurance is not a tax — but it functions a lot like one
National Insurance (NI) is a social insurance contribution, not technically a tax, though the distinction feels academic when it's being deducted from your payslip every month. The contributions you make during your working life build up your National Insurance record, and that record determines whether you qualify for the State Pension, how much of it you get, and whether you can access certain other state benefits including Jobseeker's Allowance and the New Style Employment and Support Allowance. In that sense it is insurance in the original meaning of the word: you pay in throughout your working years, and the entitlement accumulates.
The architecture of NI is more complicated than most people realise, because there are multiple classes, different rates for employees versus the self-employed versus employers, and a system of credits that can fill gaps in your record without you making any actual payments. Understanding the basics of how your record is built and how to protect it is worth the effort — a missed year or two near the start of your career can reduce your eventual State Pension by a meaningful amount.
The classes and who pays them
NI is divided into classes based on your employment situation, and each class works differently.
Class 1 is paid by employees and their employers on earnings above the Primary Threshold, which for 2026/27 sits at £12,570 per year (matching the income tax Personal Allowance). Employees pay 8% on earnings between £12,570 and £50,270, and 2% above that. Employers pay a separate Class 1 contribution at 13.8% on employee earnings above £9,100 — the Secondary Threshold. These two rates are charged on the same salary but are legally separate obligations: the employer's contribution is over and above your gross salary, not deducted from it.
Class 2 and Class 4 are paid by the self-employed. Class 2 was traditionally a flat weekly charge of a few pounds and is the contribution that builds self-employed individuals' State Pension entitlement. Following reform, Class 2 is now treated differently depending on profit levels — those earning below the Small Profits Threshold of around £6,725 can make voluntary Class 2 contributions to keep their record intact. Class 4 is a percentage-based contribution on self-employed profits above the Lower Profits Limit, currently 6% up to £50,270 and 2% above. Class 4 contributions do not build State Pension entitlement — only Class 2 does for the self-employed.
Class 3 are voluntary contributions that anyone can make to fill gaps in their NI record. The voluntary rate for 2026/27 is £17.45 per week, or around £907 for a full year. This is the mechanism for people who had periods out of work, were living abroad, or have gaps for any other reason to top up their record and protect their State Pension entitlement.
How your State Pension entitlement builds
The new State Pension (applying to people reaching State Pension age after April 2016) requires 35 qualifying years of NI contributions or credits to receive the full amount. You need at least 10 qualifying years to receive any State Pension at all. A qualifying year is one in which you paid or were credited with NI contributions for at least 52 weeks at the minimum level.
The full new State Pension in 2026/27 is worth checking on the government's website — it uprates annually under the triple lock guarantee, which increases it by whichever is highest among average earnings growth, Consumer Price Index inflation, or 2.5%. Each qualifying year you're short of 35 reduces your pension proportionally: 34 years gives you 34/35 of the full amount, and so on.
You can check your NI record and get a State Pension forecast at gov.uk/check-state-pension. This should be something you look at every few years rather than only in the run-up to retirement — gaps are much cheaper to fill via voluntary Class 3 contributions than most people expect, and HMRC sometimes allows back-filling gaps from several years prior, though the window for doing so varies depending on the circumstances and the year involved.
NI credits — the free contributions you may not know you're getting
NI credits are the mechanism by which HMRC gives you a qualifying year without you paying anything. They exist to protect the records of people who are out of paid work for reasons the state recognises as legitimate, and the list of qualifying situations is broader than most people assume.
Claiming Child Benefit for a child under 12 gives the claimant NI credits — this is significant because it means a parent who takes several years out of paid employment to care for young children can maintain their State Pension entitlement provided they are claiming Child Benefit in their own name. Parents who opted out of Child Benefit when the High Income Child Benefit Charge was introduced sometimes missed this, effectively forfeiting credits for years they were at home with children. If that applies to you, check whether a retrospective claim might be possible.
Other credit-generating situations include: receiving Jobseeker's Allowance or Employment and Support Allowance, being an approved foster carer, providing a significant amount of care to a disabled person (Carer's Credit), and certain periods of jury service. Universal Credit also generates NI credits for claimants who are not earning enough to pay contributions directly.
Employees on low incomes — the threshold trap
One situation worth knowing about specifically: if you earn between £6,396 (the Lower Earnings Limit) and £12,570 (the Primary Threshold) in 2026/27, you do not actually pay any NI — but you are treated as if you had for the purposes of building your State Pension record. This means a part-time worker earning £9,000 a year still accumulates a qualifying NI year, even though nothing appears on their payslip as an NI deduction.
Below the Lower Earnings Limit of £6,396, no qualifying year accumulates. Someone earning £6,000 per year in a single job would not build a qualifying year and would need to check whether they qualify for credits or whether making voluntary contributions makes sense.
Filling gaps — the case for reviewing your record before a deadline
HMRC periodically adjusts the window during which gaps can be filled with voluntary Class 3 contributions. The general rule allows you to fill gaps going back six tax years, but there have been extended transitional periods for gaps from earlier years in the run-up to major pension reforms. If your record has gaps from more than six years ago, it is worth checking your position sooner rather than later — the window may not remain open indefinitely.
The arithmetic of voluntary Class 3 contributions is usually straightforward to evaluate. A missing qualifying year costs roughly £907 in voluntary contributions. That year adds 1/35 of the full State Pension annually for the rest of your retirement. On current pension rates and a reasonable life expectancy, most gaps pay back the voluntary contribution within a couple of years of receiving the pension — making it one of the better-value purchases available to anyone with gaps in their record.