How to Calculate Payroll Tax for Small Businesses

Running a small business means calculating payroll tax correctly — and that means knowing what you owe to HMRC for both you and your employees. Employee income tax, National Insurance, pension contributions, and employer NI are the main pieces. Get them wrong and you face penalties; get them right and you can even claim back allowances you might not know exist.

This guide walks you through how to calculate payroll tax for small businesses step by step, with real numbers and examples.

What Is Payroll Tax?

Payroll tax in the UK has two main parts: income tax and National Insurance. They're deducted from employee pay (and you must remit them to HMRC), and you also pay employer NI on top of wages.

Income tax is straightforward in principle: it's collected via PAYE (Pay As You Earn), and employees pay based on their personal allowance and tax bands.

National Insurance is less famous but often bigger. Employee NI is 8% on earnings above £12,570 (the personal allowance threshold) and 2% above the Upper Earnings Limit. Employer NI is [STAT NEEDED: rate], charged above [STAT NEEDED: threshold].

Many small business owners are surprised by how much employer NI costs — it's often the single largest ongoing tax bill once you have employees on the payroll.

How Employees Pay Tax

Tax is deducted from each payslip based on a tax code. The standard code 1257L (2025/26) means the employee gets a personal allowance of £12,570 tax-free, then pays 20% on earnings between £12,571 and £50,270, then 40% above £50,270.

So an employee earning £40,000 per year pays:

£0 on the first £12,570
£5,486 on £27,430 × 20%
Total tax: £5,486/year, or about £457/month

That's after the personal allowance. Without it, they'd pay £8,000. The personal allowance is worth about £2,500/year in tax savings for a basic-rate taxpayer.

The key point: only income within each band is taxed at that rate. It's a marginal system, not a flat rate. This is where people get confused — earning an extra £1,000 doesn't mean you lose £400 to tax (that would be a 40% rate on the whole lot); it means you pay 40% on just that final £1,000. (Compound interest is called the eighth wonder of the world; tax bands are apparently the eighth wonder of the confusing.)

National Insurance (Employee)

Employees also pay National Insurance, which is separate from income tax. At 8% on earnings above the NI threshold, it adds about £1,920/year to our £40,000 earner.

Total take-home from £40,000:

Gross: £40,000
Less income tax: -£5,486
Less employee NI: -£1,920
Net pay: £32,594

HMRC collects both via PAYE each month, so the employee never sees the gross figure — they just see the net in their bank account.

How You Pay Employer NI

Here's where small business owners often get ambushed. Once you have employees, you pay employer NI on top of their wages. This is not deducted from what they earn; it's an extra cost you bear.

Employer NI is [STAT NEEDED: rate], charged on earnings above an annual threshold of [STAT NEEDED: threshold]. There's no upper limit — you keep paying it at that rate no matter how high wages go.

For that £40,000 employee, your employer NI bill is roughly:

(£40,000 - threshold) × [STAT NEEDED: rate] = [STAT NEEDED: amount]

That's money you have to find separately from their salary. If you employ multiple people, employer NI can quickly become your largest tax expense — which is why the Employment Allowance exists. It's a £5,000 annual credit against your employer NI bill, available to most small businesses. Claiming it can wipe out the first £5,000 of employer NI entirely.

How to Calculate Your Payroll Correctly

The process has three steps:

Step 1: Gather the information

Employees' names, addresses, National Insurance numbers
Their gross annual salary (or hourly rate × hours)
Tax code (usually 1257L, but check their P45 if they've moved jobs)
Any pension scheme they're enrolled in
Any other deductions (student loan, court order, etc.)

Step 2: Calculate net pay

Deduct income tax (use HMRC tax tables or payroll software)
Deduct employee National Insurance
Deduct any other deductions (pension, student loan repayment, etc.)
You get net pay — what hits their bank account

Step 3: Calculate your employer costs

Add employer NI (usually [STAT NEEDED]% on earnings above threshold)
Add any employer pension contributions (usually 3%+ if you auto-enrol)
This is the total cost to your business for that employee

Most small businesses use payroll software (Xero, QuickBooks, ADP, Guidepoint) to avoid manual arithmetic errors. HMRC now requires Making Tax Digital submissions, so software often syncs directly with your tax account.

The formula for net pay looks like this:

Net = Gross - Income tax - Employee NI - Other deductions

Where income tax is calculated using the tax code and earnings above the personal allowance.

Common Payroll Tax Mistakes

1. Forgetting employer NI exists Many sole traders hiring their first employee calculate wages but forget employer NI on top. Budget for [STAT NEEDED]% above the threshold, on top of every salary you pay.

2. Using the wrong tax code If someone was on code BR (emergency code, used before they've provided a P45), they pay 20% on every pound. The difference between code 1257L and BR is about £2,000/year in overpaid tax for an average earner. Check their P45 on day one.

3. Not enrolling in auto-enrolment pensions Once you have an employee, you must offer a workplace pension scheme and auto-enrol them if they're 22+, earning over £12,570 and under State Pension age. The minimum contribution is 8% of qualifying earnings (you pay 3%, they pay at least 5%). Missing this deadline leads to penalties from The Pensions Regulator.

4. Missing the employment allowance If you qualify for Employment Allowance, not claiming it means leaving up to £5,000 on the table each year.

5. Paying PAYE late Payroll payments are due to HMRC on the 19th of each month (or 22nd if you pay electronically). Late payment attracts penalties and interest. Mark it in your calendar or set a reminder.

6. Overlooking small business tax deductions Many business owners pay more tax than they need to because they don't claim allowable expenses — working from home, professional subscriptions, equipment, insurance, training. The more you can claim legitimately, the lower your taxable profit and your corporation tax bill.

Tools and Next Steps

For sole traders and self-employed people not running a formal payroll, you also owe Class 2 and Class 4 National Insurance. Class 2 is a flat [STAT NEEDED] per week; Class 4 is [STAT NEEDED]% on profits between £12,570 and £50,270, then [STAT NEEDED]% above that. See our guide on how to calculate Class 2 and Class 4 NI.

If you operate as a limited company, you likely pay corporation tax on profits, which opens other strategies — like paying yourself dividends, which carry different tax treatment. And don't overlook business asset depreciation, which reduces your taxable profit.

For payroll specifically, use the sales tax calculator to sense-check your deductions, or explore our full calculator suite to understand PAYE, pension planning, and tax liability.

Frequently Asked Questions

Q: What's the difference between income tax and National Insurance? A: Income tax and National Insurance are two separate taxes collected together via PAYE. Income tax funds the NHS and public services; NI funds state pensions and some benefits. They're calculated on different thresholds (personal allowance vs. NI threshold) and at different rates. For 2025/26, you might pay 20% income tax but 8% NI on the same pound of earnings. HMRC bundles them together on payslips for simplicity, but they're different taxes.

Q: Do I have to use payroll software? A: For one or two employees, a careful spreadsheet can work, but payroll software is cheaper than the admin time it saves — and it reduces errors. For three or more employees, software pays for itself. HMRC requires Making Tax Digital submissions, and most software handles that automatically. Start with free options or low-cost tiers before graduating to Xero or QuickBooks.

Q: Can I claim back overpaid tax? A: Yes. Check your tax code on your payslip and your P60 at year-end. If you've been on the wrong code, you can claim a refund via your tax return or by contacting HMRC. If you're owed money, HMRC usually processes it within a few weeks. Keep payslips for your records — they're your proof of what you paid.

Q: What happens if I make a payroll mistake? A: Small errors (a few pounds) are usually fine. Large errors (wrong tax band or missing an employee entirely) trigger corrections and possible penalties. If you catch it early and report it to HMRC proactively, penalties are often reduced or waived. Check out our guide to HMRC tax enquiries for more detail on what to expect if HMRC reviews your payroll.

Q: Is there any way to reduce my employer NI bill? A: Yes — claim Employment Allowance if you qualify (most small businesses do). It's a £5,000 annual credit. Alternatively, consider whether your business structure suits a limited company vs. sole trader — corporation tax is calculated differently, and sometimes dividends are cheaper than salary. Talk to an accountant about your specific situation.

Q: What if I have a seasonal business or employees who leave partway through the year? A: PAYE and NI are calculated on whatever you actually paid them. If someone left halfway through, you calculate their share of the annual thresholds (personal allowance, NI threshold) based on the time they worked. Issue them a P45 when they leave and file a final return with HMRC. Payroll software handles this automatically.

Q: Do I need to keep payroll records? A: Yes. Keep payslips, P45s, pension records, and all HMRC correspondence for at least 6 years. Scans are fine; paper records aren't required. Digital records satisfy HMRC's requirements.