What do the UK National Insurance category letters mean?

TL;DR

Each UK employee is assigned a single-letter National Insurance category that tells payroll which employee and employer NI rates apply. Based on HMRC guidance for 2026/27, the standard employee rate is 8% between £12,570 and £50,270 and 2% above, with employers generally paying 13.8% above £9,100 - adjusted by category.

In one sentence

A National Insurance category letter is HMRC's instruction to payroll about which NI rates apply to a worker based on age, status and scheme.

In plain English

Your NI category determines the rates payroll uses. Most employees sit on category A, paying 8% employee NI between the Primary Threshold (£12,570) and the Upper Earnings Limit (£50,270), and 2% above. Employers pay 13.8% above the Secondary Threshold (£9,100) for most categories, though many categories provide employer relief.

Categories exist to encourage employment of certain groups (apprentices, under-21s, veterans), to handle people over State Pension age, to manage deferral when working multiple jobs, and to apply geographic incentives within freeports and investment zones. The numbers underneath are the same; what changes is who pays what.

Errors here are usually about the wrong letter being used - for example, an under-21 left on A instead of M, or a veteran left on A instead of V. These do not change your take-home pay, but they affect what your employer pays and what you can check is correct.

It is worth understanding the relationship between the category and the underlying thresholds. Based on HMRC publications for 2026/27, the Primary Threshold (where employee NI starts) is £12,570, the Upper Earnings Limit is £50,270, and the Secondary Threshold (where employer NI starts) is £9,100. Several categories have their own upper thresholds for the employer-side relief - the Upper Secondary Threshold for under-21s (UST), the Apprentice Upper Secondary Threshold (AUST), the Veterans' Upper Secondary Threshold (VUST), and the Freeport Upper Secondary Threshold (FUST). Above each of those, the standard 13.8% employer rate kicks in. The employee figures are independent of these and follow the Primary Threshold and Upper Earnings Limit rules described above.

Categories also interact with deferment. If you have two jobs and your combined earnings appear consistent with paying NI twice on the same band, you can apply to defer NI on the secondary employment. Categories J (adult), L (freeport adult) and Z (under-21) reflect this deferment. The effect is that the secondary employment pays only 2% on earnings above the Primary Threshold rather than 8%, with HMRC reconciling the position after year-end. This does not prove you will save tax - it appears consistent with smoothing the cashflow and avoiding small overpayments mid-year.

Category table - 2026/27 rates

The figures below appear consistent with the HMRC NI rates and thresholds tables published for 2026/27.

Category	Who it applies to	Employee NI	Employer NI
A	Standard adult employees 21+ to State Pension age	8% / 2%	13.8% above ST
B	Married women / widows with reduced rate election	1.85% / 2%	13.8% above ST
C	Employees over State Pension age	0%	13.8% above ST
F	Standard adults working in a freeport	8% / 2%	0% up to FUST
H	Apprentices under 25	8% / 2%	0% up to AUST
I	Married women / reduced rate working in a freeport	1.85% / 2%	0% up to FUST
J	Employees deferring NI (multiple jobs)	2%	13.8% above ST
L	Deferred NI - freeport workers	2%	0% up to FUST
M	Employees under 21	8% / 2%	0% up to UST
S	Over State Pension age in a freeport	0%	0% up to FUST
V	Qualifying veterans, first year of civilian employment	8% / 2%	0% up to VUST
X	No NI due (e.g. under 16)	0%	0%
Z	Under 21, deferring NI	2%	0% up to UST

ST = Secondary Threshold (£9,100). UST = Upper Secondary Threshold for under-21s. AUST = Apprentice Upper Secondary Threshold. FUST = Freeport Upper Secondary Threshold. VUST = Veterans' Upper Secondary Threshold. Figures based on HMRC tables for 2026/27.

Worked example (2026/27 figures)

Liam, 19, earns £30,000 on category M. Employee NI: (£30,000 − £12,570) × 8% = £1,394.40 per year, or about £116.20 per month. Employer NI is 0% on earnings up to the Upper Secondary Threshold for under-21s; above that threshold the employer pays 13.8%. Liam's take-home appears identical to a category A worker; the saving is on the employer side.

A second scenario. Aisha is 67, has reached State Pension age, and continues to work earning £24,000 on category C. Employee NI is 0% across all bands, so she keeps the full £24,000 less income tax: (£24,000 − £12,570) × 20% = £2,286 in tax. Her employer still pays employer NI of 13.8% above £9,100. If payroll left Aisha on category A by mistake, she would be deducted (£24,000 − £12,570) × 8% = £914.40 of NI in error. Based on HMRC guidance, payroll can correct the category and refund the deduction in the following pay run, with year-end reconciliation catching anything missed.

A third scenario. Dev is a qualifying veteran in his first year of civilian employment, earning £45,000 on category V. Employee NI is identical to category A: (£45,000 − £12,570) × 8% = £2,594.40 per year. Employer NI is 0% up to the Veterans' Upper Secondary Threshold and 13.8% above. The relief lasts for the first 12 months of civilian employment from the first qualifying day. If the employer left Dev on category A, his take-home would be unchanged - but the employer would lose the relief. This worth reviewing because the employer benefits, not Dev directly.

A fourth scenario. Priya works two jobs: Job 1 earns £45,000 on category A, Job 2 earns £15,000 on category J (deferred). Job 1 deducts (£45,000 − £12,570) × 8% = £2,594.40. Job 2, on category J, deducts only 2% on the slice above the Primary Threshold each pay period - broadly £15,000 ÷ 12 minus £1,047.50 = £202.50 per month at 2% = £4.05/month, or roughly £49 a year. Without deferment, Job 2 would have applied 8% across that band as well, producing a larger deduction and a likely refund at year-end. This appears consistent with HMRC's smoothing approach.

Common mistakes people make

Reading the NI category as if it changes employee take-home for under-21s and apprentices - for most bands it does not.
Confusing category B (reduced rate) - it applies only to women with a historical election still in force.
Assuming category C means no NI at all - employers still pay employer NI.
Missing veterans' relief by leaving a qualifying veteran on category A.
Leaving an apprentice on A after they turn 25 - should move to A or another adult code.
Using deferment categories (J, L, Z) without an active CA2700 deferment certificate from HMRC.
Confusing the NI category letter with the tax code letter - they are separate systems with different purposes.
Assuming the freeport categories apply to anyone working near a freeport; they apply only to qualifying employments at registered freeport sites.
Forgetting to update the category when a worker reaches State Pension age - the change should happen from the next pay period after the birthday.

When this might apply to you

You turned 21 - category may need to move from M/Z to A/J.
You started an apprenticeship and your employer can use H.
You reached State Pension age - category should move to C.
You took a second job and want to defer NI on one - categories J, L or Z.
You are a recent service leaver eligible for V.
You started work at a registered freeport site and your employer is eligible to apply category F, I, S or L.
You are under 16 and earning above the threshold - category X confirms no NI is due.
You finished an apprenticeship at age 24 and the category should move from H to A.

What to do if your category looks wrong

Locate the single-letter NI category next to the NI line on your payslip.
Compare your payslip's NI letter against the HMRC category list for 2026/27.
Confirm your eligibility - age, apprenticeship status, veteran status, deferment, freeport employment, or State Pension age.
Speak to payroll - only the employer can change the category in their system.
Provide evidence (e.g. apprenticeship agreement, veteran ID, deferment certificate CA2700, proof of age) where required.
If deferment is required, apply to HMRC using the appropriate form before payroll changes the category.
Check the correction in the next payroll run; the NI line should appear consistent with the new category.
Keep a record of pre- and post-correction payslips in case a year-end reconciliation is required.
Use our payslip checker to compare gross-to-net figures against the 2026/27 thresholds.

When to contact HMRC, payroll, or a professional

Payroll is the right first contact for an apparent category error. HMRC issues deferment certificates for category J/Z and can confirm State Pension age for category C. A tax adviser may help if multiple employments mean you are paying NI above the annual maximum.

Frequently asked questions

What is the most common NI category?

Category A is the standard letter for most employees aged between 21 and State Pension age.

Why am I on category C?

Category C typically applies to employees over State Pension age, who pay no employee NI but whose employer still pays employer NI.

What does category H mean?

H usually denotes apprentices under 25 - employer NI is reduced to 0% up to the relevant threshold.

Are M and Z categories the same as A but for under-21s?

Broadly yes - M for under-21s, Z for under-21s deferring NI; both reduce employer NI up to the upper secondary threshold.

What is category V?

V applies to qualifying veterans during their first year of civilian employment, with employer NI relief up to the veterans' upper secondary threshold.

Do freeport and investment-zone categories exist?

Yes - categories F, I, S and L apply within freeports and investment zones; the exact code depends on age and deferral status.

Where do I find my NI category on my payslip?

It appears next to the NI line, usually as a single letter such as A, M, H, C or X.

Does the NI category change my take-home pay?

For most employees the category does not change take-home pay - employee rates of 8% and 2% apply identically across categories A, M, H, V and similar. Categories B, C, J and Z change the employee rate, so take-home may differ.

What happens to my NI category when I turn 21?

Your employer should move you from M (or Z) to A (or J), based on HMRC guidance. Take-home is unchanged in most cases, but the employer NI cost rises above the Upper Secondary Threshold for under-21s.

Can I be on more than one category at once?

Not for the same employment in the same period - each employment has one category. If you have two jobs, each may have a different category, and deferment categories J, L or Z may apply if you elect to defer NI on the secondary.

How do I claim back NI if I have paid above the annual maximum?

Based on HMRC guidance, you can apply for a refund using form CA5610 if your contributions across multiple jobs appear consistent with exceeding the annual maximum. This does not prove a refund is automatic; HMRC reviews each case on its facts.

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Educational content only; not regulated tax advice.