Have you ever wondered why your payroll costs feel disproportionately high compared to the salaries you pay? The culprit is usually National Insurance Contributions (NI), a levy that hits employers harder than most business owners realise. Unlike income tax, NI is not a single charge; it is a layered system of payments that employees, employers, and the self-employed make to fund the State Pension, the NHS, and statutory benefits such as sick pay and maternity leave.
For a UK business, the biggest sting is Class 1 Secondary NI. As an employer, you pay 15% on every pound an employee earns above the secondary threshold of £5,000 per year (2026/27). There is no cap, so a senior engineer on a £60,000 salary costs you an additional £8,250 in employer NI alone (£55,000 x 15%). This is a direct hit on your bottom line, not an optional overhead.
Your employees also contribute via Class 1 Primary NI: 8% on earnings between the primary threshold (£12,570) and the upper earnings limit (£50,270), then 2% above that. You must deduct this through PAYE and report it monthly via RTI (Real Time Information). A common mistake is forgetting that employer NI is due on benefits in kind, such as company cars or private medical insurance, which can catch out manufacturing SMEs or professional services firms that offer these perks.
If you are a sole trader running a plumbing business or a consultancy, your NI treatment is different. You can pay Class 2 NI voluntarily at £3.65 per week (2026/27) if your profits fall below the Small Profits Threshold of £7,105; those with profits above that threshold receive NI credits automatically without paying Class 2. You also pay Class 4 NI at 6% on profits between £12,570 and £50,270, then 2% above that (2026/27). For limited company directors, the standard tax planning move is to pay yourself a salary above the secondary threshold of £5,000 but below the primary threshold of £12,570, then extract the rest as dividends. However, dividends do not count towards NI, so you may miss out on contribution-based benefits like the State Pension. This trade-off is worth modelling carefully.
When hiring contractors, watch out for IR35. If HMRC decides a contractor is a disguised employee, you become liable for their employer NI plus interest and penalties. This is a particular risk for hospitality operators and e-commerce sellers who engage freelancers for short-term projects. Always use HMRC's Check Employment Status for Tax (CEST) tool or seek professional advice before engaging a worker outside PAYE.
Why this matters for your business: NI is typically your second largest employment cost after salaries. Getting the structure wrong can cost thousands. For example, a software company with five employees each on £45,000 will pay roughly £30,000 in employer NI annually (five employees x £40,000 above the £5,000 threshold x 15%), before the Employment Allowance of up to £10,500 is applied. Shifting that cost into dividend payments or salary sacrifice schemes can save a significant sum, but you must stay within the rules. Always factor NI into your pricing model: if you quote a client £150 per hour, roughly £22.50 (15%) of that goes to employer NI in respect of the employee cost before you see any profit. Plan accordingly.