How National Insurance Is Calculated in the UK
National Insurance contributions fund the UK's state pension, the NHS and other welfare payments. From 6 April 2026 the employer rate rose to 15%, the largest single increase in over a decade, costing businesses hundreds of pounds more per employee each year [1] [4]. Understanding exactly how the calculation works is no longer a matter of payroll administration alone; it drives hiring costs, reliefs strategy and cash-flow planning.
National Insurance is split into classes. The class paid depends on whether the worker is employed or self-employed, and on how much they earn. For most payroll scenarios the relevant class is Class 1, which covers employee contributions deducted through PAYE and employer contributions paid directly to HMRC [2].
This article walks through the step-by-step Class 1 calculation for employees and employers, covers the 2026-27 thresholds, explains NI category letters, zero-rate reliefs and Employment Allowance, and sets out the special annual earnings period that applies to company directors.
Key takeaways
- Employer NI is charged at 15% on employee earnings above £5,000 per year from 6 April 2026, up from the previous 13.8% rate.
- Employees pay 8% NI on earnings between £12,570 and £50,270, then 2% above the Upper Earnings Limit.
- The NI category letter assigned to each employee determines both the employee and the employer rates.
- Several reliefs reduce employer NI to 0% for specific groups: employees under 21, apprentices under 25 and armed forces veterans in their first year of civilian employment.
- Employment Allowance of £10,500 offsets employer NI for most eligible businesses each tax year.
How National Insurance contributions are classified
National Insurance is not a single percentage on gross pay. It is divided into classes, each designed for a different group of taxpayers. The table below shows the classes most relevant to payroll in the 2026-27 tax year [2] [7].
| Class | Who pays | How it is collected |
|---|---|---|
| Class 1 (primary) | Employees | Deducted from wages via PAYE |
| Class 1 (secondary) | Employers | Paid alongside the PAYE bill |
| Class 1A | Employers | On benefits in kind, reported via P11D |
| Class 2 | Self-employed (voluntary) | Via Self Assessment |
| Class 4 | Self-employed | Via Self Assessment |
Class 1A is charged at 15% on the taxable value of benefits in kind provided to employees, and on termination awards exceeding £30,000 [12] [13]. The remainder of this article focuses on Class 1 for employed workers and Class 4 for the self-employed.
The earnings thresholds that govern Class 1 NI
The Class 1 calculation rests on four thresholds. Each one triggers a change in the contribution rate. The figures below are drawn from HMRC NI Guidance for software developers, effective 6 April 2026 [3] [4].
| Threshold | Weekly | Monthly | Annual |
|---|---|---|---|
| Secondary Threshold (ST), employer trigger | £96 | £417 | £5,000 |
| Lower Earnings Limit (LEL) | £129 | £559 | £6,708 |
| Primary Threshold (PT), employee trigger | £242 | £1,048 | £12,570 |
| Upper Earnings Limit (UEL) | £967 | £4,189 | £50,270 |
One widely misunderstood detail: the Secondary Threshold (£5,000) sits well below the Primary Threshold (£12,570). Employers therefore pay NI on the band between £5,000 and £12,570, even though employees owe nothing on those earnings [5].
How employee National Insurance is calculated step by step
Employee contributions are primary Class 1 NICs, calculated using the exact percentage method and applied to earnings in each pay period [5] [14].
The rates for a standard Category A employee (most employees aged 21 to State Pension age) in the 2026-27 tax year are:
| Earnings band | Employee rate |
|---|---|
| Below the LEL | 0% |
| LEL to Primary Threshold | 0% |
| Primary Threshold to UEL | 8% |
| Above the UEL | 2% |
A worked example clarifies the arithmetic. An employee on a monthly salary of £3,500 sits below the monthly UEL of £4,189 and above the monthly Primary Threshold of £1,048. The employee NI due is: £3,500 minus £1,048, which equals £2,452, multiplied by 8%, giving £196.16. The payroll run deducts this from gross pay and records it alongside the Income Tax deduction on the employee's payslip. HMRC-recognised UK payroll software applies the exact percentage method and rounds each NIC figure to the nearest penny.
How the calculation changes above the Upper Earnings Limit
For higher earners, the rate above the UEL drops to 2% rather than 8% [6] [3]. For an employee earning £65,000 per year, the calculation splits across two bands: 8% applies to the £37,700 between the Primary Threshold and the UEL, giving £3,016; and 2% applies to the £14,730 above the UEL, giving £294.60. Total employee NI for the year is £3,310.60.
How employer National Insurance is calculated step by step
Employer NICs (secondary Class 1) are an additional cost to the business and are not deducted from the employee's wages. The Secondary Threshold in the 2026-27 tax year is £5,000 per year (£417 per month) [4] [15].
The employer rate is 15% on all earnings above the Secondary Threshold. Unlike the employee calculation, there is no reduced upper-band rate. The same 15% applies whether the employee earns £25,000 or £250,000 per year.
Taking the same example of a monthly salary of £3,500: the employer subtracts the monthly Secondary Threshold of £417, leaving £3,083, and multiplies that by 15%. The employer NI due is £462.45. This amount is paid to HMRC alongside the employee's Income Tax and primary NIC each month. For any business managing small business payroll, the employer NI bill is now the largest single payroll tax line.
Employment Allowance: the main offset available to employers
Eligible employers can claim Employment Allowance of £10,500 per tax year against their employer NI liability [9]. The allowance is applied period by period until the full £10,500 has been offset. Critically, it must be claimed afresh each April by submitting an Employer Payment Summary (EPS); it does not roll forward automatically from the prior year [9] [15].
Sole directors with no other employees cannot claim Employment Allowance, nor can companies where more than half their work is carried out for a public-sector body.
NI category letters: how the letter changes the rate
Every employee on a UK payroll must be assigned an NI category letter. The letter governs the exact employee and employer rates applied in each payrun [8]. Assigning the wrong letter is one of the most common payroll errors and can lead to either an underpayment or an overpayment of NI.
| Letter | Employee group | Employee rate | Employer rate up to £50,270 |
|---|---|---|---|
| A | Standard (21 to State Pension age) | 8% / 2% | 15% |
| B | Married women with valid reduced-rate election | 1.85% / 2% | 15% |
| C | At or above State Pension age | 0% | 15% |
| M | Employees under 21 | 8% / 2% | 0% |
| H | Apprentices under 25 | 8% / 2% | 0% |
| V | Armed forces veterans (first 12 civilian months) | 8% / 2% | 0% |
Category M, H and V attract zero employer NI on earnings up to the Upper Secondary Threshold of £50,270 [3]. For an employer paying a 20-year-old £28,000 per year, the saving under Category M versus the standard Category A rate amounts to £3,450 per year (£28,000 minus £5,000, multiplied by 15%). Accountants managing payroll across multiple clients should confirm category letter assignments at each new-starter onboarding. A multi-client payroll dashboard surfaces NI category as part of the employee setup workflow, reducing the risk of an incorrect letter persisting across multiple payruns.
Self-employed National Insurance: Classes 2 and 4
Self-employed individuals do not pay Class 1 NI. Their contributions fall under Class 2 and Class 4, both collected through Self Assessment rather than PAYE [10].
| Class | Rate | Trigger |
|---|---|---|
| Class 2 | £3.65 per week (treated as paid) | Profits above £12,570 |
| Class 4 | 9% up to £50,270; 2% above | Profits above £12,570 |
Class 2 contributions are now treated as having been paid automatically for most self-employed individuals, removing the previous requirement for a voluntary payment to protect state pension entitlement [10]. Class 4 is assessed on net trading profits and declared in the annual Self Assessment return. For individuals moving between employment and self-employment in the same tax year, understanding the difference between the two systems is essential; the article on PAYE versus self-assessment covers the transition in detail.
How directors' NI is calculated differently
Company directors use an annual earnings period rather than a per-period calculation [11]. Their NI is assessed on total cumulative earnings across the whole tax year, using the annual thresholds, not on the weekly or monthly figures applied to standard employees.
This reflects the common director pattern of taking a low regular salary topped up by a dividend or bonus later in the year. Under the annual method, a director receiving £1,000 per month and a bonus of £30,000 in March cannot benefit from per-period thresholds that would otherwise understate the NI liability. The payroll software calculates NI on cumulative earnings to date each time the director is paid, and adjusts the amount due accordingly [11]. For directors appointed mid-year, the annual thresholds are pro-rated by the number of remaining weeks in the tax year. Platforms integrating payroll via a HMRC-recognised payroll API must handle the director annual-earnings period as a distinct calculation mode, not as a variant of the standard employee calculation.
Conclusion
National Insurance is a banded system built on four thresholds, with separate rate structures for employees and employers, distinct rules for the self-employed and directors, and a set of category letters that can reduce the employer's contribution to zero for qualifying workers. The Employment Allowance, the Category M and H zero rates and the veterans relief together represent thousands of pounds in legitimate savings for businesses that apply them correctly.
The 15% employer rate and the reduced Secondary Threshold that came into force from 6 April 2026 widened the gap between what employees see on their payslips and what the employer's true payroll cost is. For any business that has not reviewed its payroll setup since that date, confirming the correct NI category for each employee and submitting a fresh Employment Allowance claim via EPS is the most immediate way to ensure the calculation is right.
Frequently asked questions
How is National Insurance calculated on a monthly salary?
For a standard Category A employee, the monthly calculation subtracts the monthly Primary Threshold (£1,048 in the 2026-27 tax year) from gross pay and applies 8% to the excess, up to the monthly Upper Earnings Limit of £4,189. Earnings above £4,189 attract 2% instead. For the employer, gross pay above the monthly Secondary Threshold of £417 is multiplied by 15%. Payroll software performs these steps automatically each period and rounds each figure to the nearest penny.
What is the difference between employee and employer National Insurance?
Employee National Insurance (primary Class 1) is deducted from the employee's wages before they are paid, and it builds entitlement to the state pension and other contributory benefits. Employer National Insurance (secondary Class 1) is an additional cost borne entirely by the employer and paid separately to HMRC; it does not reduce the employee's take-home pay. The two contributions also use different starting thresholds: employees begin paying above £12,570 per year, while employers begin above £5,000 per year in the 2026-27 tax year.
Does every employee pay the same rate of National Insurance?
No. The NI category letter assigned to each employee determines the rates applied. Most employees aged 21 to State Pension age use Category A and pay 8% between the Primary Threshold and the Upper Earnings Limit. Married women holding a valid reduced-rate election use Category B and pay 1.85% on the same band. Employees who have reached State Pension age are assigned Category C and pay no employee NI at all, though the employer continues to pay 15% on their earnings above the Secondary Threshold.
How does director NI differ from standard employee NI?
Directors are subject to an annual earnings period under HMRC rules, meaning their NI is assessed on cumulative earnings for the full tax year rather than on each individual pay period. This prevents directors from exploiting per-period thresholds by concentrating pay at the end of the year. Payroll software must support the annual method as a distinct calculation mode: it recalculates NI on the cumulative year-to-date total each time the director receives a payment, then deducts contributions already paid in earlier periods to arrive at the amount due for the current payrun.
