A job and a side business: how the tax fits together

A second employment and a sole-trader business are different. An employer normally runs PAYE and Class 1 NI; a sole trader reports the relevant business profit. Calling a payment “freelance” does not by itself establish employment status.

Keep the engagement details, contract and actual working arrangement. Use the two-jobs calculator for two ordinary employments. Use the self-employed tool for a supported sole-trader activity alongside employment. A limited company or partnership needs its own rules.

For Income Tax, add the relevant employment income and business profit. Do not give each its own £12,570 Personal Allowance. The job may already use that allowance, so extra profit can fall directly into an Income Tax band.

PAYE tax already deducted is a credit against the annual bill, not a deduction from income. Business turnover is not the same as profit: subtract the eligible expense or trading-allowance route before combining the income. Scottish taxpayers use Scottish rates on these non-savings sources.

Assume England in 2026/27, the standard allowance and no other adjustments. Business receipts are £6,000 and allowable costs are £2,000, giving £4,000 profit. Income Tax on £30,000 employment alone is £3,486. On combined £34,000 income it is £4,286.

The business therefore adds £800 Income Tax. Its £4,000 profit is below the ordinary Class 4 starting point, so no Class 4 is due on it. Business cash after the £2,000 costs and £800 extra tax is £3,200, before any loan or other personal effects. Any employee NI on the existing job remains separate.

Class 1 is assessed on employment earnings. Class 4 uses qualifying self-employed profit. Where both apply, regulation 100 can reduce Class 4 through an annual maximum. It does not mean all business profit becomes NI-free when you have a job.

The calculation needs employee Class 1 paid at the main rate, excluding the 2% part and employer NI. A P60’s total NI figure is not necessarily that input. Ask payroll for the breakdown if the records do not identify it.

As a Class 4-only illustration, £20,000 profit ordinarily gives £445.80 Class 4. With £3,000 main-rate Class 1 already paid, the maximum calculation leaves a 2% charge on £7,430, or £148.60. The complete annual return still needs your actual income and other facts.

A Self Assessment loan calculation can combine employment and business income and credit PAYE loan repayments. Its annual employment amount uses the SA110 calculation, starting with taxable employment income and adjusting for the specified exclusions and employment expenses. Payroll deductions use a separate earnings basis. Do not add net-pay pension contributions back to P60 taxable pay for the annual calculation.

For example, £40,000 employment pay with £4,000 net-pay pension contributions leaves £36,000 taxable pay. Add £10,000 business profit, with no other adjustments, and annual SA loan income is £46,000. For Plan 2 in 2026/27, (£46,000 − £29,385) × 9% rounds down to £1,495 before PAYE loan credits. A separate eligible relief-at-source pension contribution is deducted once in the SA loan calculation.

Keep undergraduate and postgraduate deductions separate. Unearned income above £2,000 can bring its whole amount into the SA loan calculation, including relevant interest or dividends. Do not subtract £2,000 as if it were an allowance, and do not count voluntary repayments as ordinary PAYE deductions.

Collect the P60 or relevant final payslips/P45, taxable benefits, employment loan-earnings figure, main-rate Class 1, tax deducted, student and postgraduate loan totals, business receipts and expenses, and payments on account already made. Keep dates and tax years attached to each total.

Ask a precise question when a field is missing: “For 2026/27, how much employee Class 1 did I pay at the main rate, excluding the 2% portion?” The supported calculator then separates total liability, tax attributable to the business and the remaining balance. HMRC’s actual statement remains the payment reference.