National Insurance Contribution Categories

National Insurance contribution categories are the classifications that determine how much National Insurance (NI) an individual and their employer pay, and on what basis. National Insurance is a UK payroll tax administered by HMRC that funds the State Pension and contributory benefits, and it is not applied at a single uniform rate – liability depends on the type of contributor and on the individual’s personal circumstances.

The term is used loosely to describe two distinct systems, and separating them is the first step to using it correctly:

• Contribution classes (Class 1, 1A, 1B, 2, 3, 4) categorise contributions by type of contributor and payment – employed, self-employed, voluntary, or employer-paid on benefits.
• Category letters (A, B, C, and so on) sit inside Class 1 and categorise individual employees by age, gender-historic election, pension-age status, deferment, or location, determining which rates and thresholds payroll applies to that person.

In a payroll context, “NI category” almost always means the second: the single letter held against each employee’s record.

The contribution classes

Class 1 is the main employment class, split into a primary contribution deducted from the employee’s pay and a secondary contribution paid by the employer on top of salary. This is what runs through PAYE each pay period.

Class 1A is an employer-only charge on most taxable benefits in kind – company cars, private medical cover, and similar – as well as on certain termination payments above the tax-free threshold. It is paid annually rather than per pay period.

Class 1B is an employer-only charge on items settled through a PAYE Settlement Agreement.

Class 2 applies to the self-employed. Mandatory Class 2 was abolished from April 2024, but it remains available as a voluntary contribution for those wanting to protect their State Pension record, at £3.65 a week for 2026/27.

Class 3 is the voluntary class used to fill gaps in a contribution record where no other class applies.

Class 4 applies to self-employed profits, charged at 6% between the lower and upper profit limits and 2% above.

The category letters

Every employee on a UK payroll carries one Class 1 category letter, and it drives the calculation. The letters are easier to understand grouped by how they behave than listed alphabetically.

Standard treatment – A, and its variants F, H, M, N, V. Letter A is the default for most employees: 8% employee contributions on earnings between the Primary Threshold and the Upper Earnings Limit, then 2% above, with the employer paying 15% on everything above the Secondary Threshold. The variants carry the same employee rate but change the employer’s position. H covers apprentices under 25, M covers employees under 21, and V covers qualifying veterans in their first civilian employment – for all three, employer NI is 0% up to the relevant upper secondary threshold and 15% only above it. F and N are the equivalents for Freeport and Investment Zone employment, where employer relief runs up to a lower threshold.

Reduced employee rate – B, E, I. These apply to a shrinking group of married women and widows holding a historic reduced-rate election, who pay 1.85% rather than 8% on the main band and 2% above the Upper Earnings Limit. E and I are the Investment Zone and Freeport equivalents.

No employee contributions – C, K, S, X. Letter C covers employees over State Pension age, who stop paying employee NI entirely while the employer continues to pay its share. K and S are the Investment Zone and Freeport equivalents. X covers employees with no NI liability at all, such as those under 16.

Deferment – J, D, L, Z. These apply where an employee has more than one job and has been granted deferment because they are already paying enough NI elsewhere. They pay a flat 2% on earnings above the Primary Threshold instead of the main 8% rate. Z is the under-21 version, which also carries the employer relief; D and L are the Investment Zone and Freeport equivalents.

The pattern worth internalising is that a letter encodes two separate pieces of information at once – what the employee pays, and what the employer pays. Two letters can look similar on the employee side while producing very different employer costs.

Rates and thresholds for 2026/27

For the tax year running 6 April 2026 to 5 April 2027:

• Employee Class 1: 8% on earnings between the Primary Threshold of £12,570 and the Upper Earnings Limit of £50,270 a year, then 2% above
• Employer Class 1: 15% on earnings above the Secondary Threshold of £5,000 a year, with no upper limit
• Lower Earnings Limit: £6,708 a year. No contributions are due at this level, but earnings at or above it still count as a qualifying period towards the State Pension
• Upper Secondary Threshold (and its apprentice and veteran equivalents): £50,270 a year – the point at which employer relief for letters H, M, V and Z ends
• Freeport and Investment Zone employer relief threshold: £25,000 a year
• Class 1A and Class 1B: 15%
• Employment Allowance: up to £10,500 off the employer NI bill for eligible employers

The 15% employer rate and £5,000 Secondary Threshold, introduced in April 2025 in place of 13.8% and £9,100, are unchanged for 2026/27. Because that threshold is now low, employer NI is charged on a much larger share of most salaries than it was before, which is what makes category letters and Employment Allowance eligibility materially more valuable than they used to be.

Why the category letter matters operationally

A category letter is a live payroll control, not a static piece of reference data. It has to reflect an employee’s circumstances at each pay run, and those circumstances change mid-year: an employee turns 21, an apprentice passes 25 or finishes their programme, someone reaches State Pension age, a veteran’s qualifying period ends, deferment is granted or withdrawn.

When a letter is wrong, the error is usually silent and systematic. Leaving an employee on M after their twenty-first birthday understates employer NI and creates an underpayment to correct; applying A to someone who should be on C over-deducts from the employee. Because the letter is applied automatically by payroll software to every affected pay period, a single misclassification compounds across the year and, replicated across a workforce, becomes a significant reconciliation exercise.

Directors add a further layer, since their NI is normally calculated on an annual earnings period rather than per pay period, which changes the timing of contributions even when the letter is correct.

Mercans provides managed payroll, EOR, and global payroll technology in the UK and more than 160 countries, maintaining category letters and threshold logic through mid-year status changes, applying Employment Allowance and Class 1A treatment correctly, and filing RTI submissions to HMRC – so classification errors are caught before they accumulate across pay periods.

Frequently asked questions

What is the difference between an NI class and an NI category letter?

A class describes the kind of contribution: Class 1 for employment, Class 1A for benefits in kind, Class 4 for self-employed profits, and so on. A category letter sits inside Class 1 and identifies which set of rates and thresholds applies to a specific employee. An employee is in Class 1 and holds a category letter; the two are not alternatives.

Which category letter applies to most employees?

Letter A. It is the default for employees aged 21 to State Pension age with no deferment, reduced-rate election, or special status, and it applies to the large majority of a typical UK payroll.

Do employees stop paying National Insurance at State Pension age?

Employees do, but employers do not. Once an employee reaches State Pension age their category letter changes to C (or the Freeport or Investment Zone equivalent), and employee contributions cease. The employer continues to pay its 15% secondary contribution on earnings above the Secondary Threshold. Forgetting the second half of that is a common source of over-deduction.

What happens if the wrong category letter has been used?

The liability has to be corrected. Depending on when the error is found, this may mean adjusting within the same tax year through payroll, or submitting an amended Full Payment Submission for a closed year. Under-deducted employee contributions and under-paid employer contributions both remain due, and interest or penalties can apply, so the practical priority is identifying the point at which the classification became wrong rather than only fixing it going forward.

Are the under-21 and apprentice reliefs a reduction in employee National Insurance?

No. Employees on letters M and H pay the standard employee rates. The relief is entirely on the employer side: no secondary contributions up to the upper secondary threshold, then 15% above it. This is why the reliefs reduce the cost of employing younger workers and apprentices without changing their take-home pay.

Where can an employee find their category letter?

It appears on the payslip, alongside the NI deduction. Employees who believe theirs is wrong – for example after a birthday that should have triggered a change – should raise it with payroll, since the letter is maintained by the employer rather than set by the employee.