Why is my payslip different from the calculator?

PAYE works one pay period at a time

Under PAYE an employer takes income tax and National Insurance before paying wages, and the tax code tells them how much. Income tax is usually worked out on total income so far in the tax year, so a bonus, overtime or unpaid leave changes that month's tax. National Insurance is charged on each week's or month's pay. The calculator applies 8% between £12,570 and £50,270 a year and 2% above; payroll applies the weekly or monthly equivalents of those limits, so one large month is not charged the same as twelve even ones.

Your tax code carries adjustments

The calculator assumes 1257L unless you enter another code. HMRC changes a code when income or circumstances change: gov.uk lists a new job, a second job or pension, taxable state benefits, savings interest above the Personal Savings Allowance, starting or stopping benefits from a job, Marriage Allowance, expenses with tax relief, the High Income Child Benefit Charge collected through pay, and tax owed from being on the wrong code. A code that ends in W1, M1 or X is an emergency code, taxed on each payslip alone.

Three pension methods, three payslips

The same 5% contribution of £1,750 a year gives three results, depending on how the scheme takes it.

• Salary sacrifice. An agreement to give up part of cash pay in return for a non-cash benefit, here an employer pension contribution. Tax and National Insurance are worked out on the lower pay.
• Net pay. The employer takes the contribution before pay is taxed, so tax is due on what is left. The National Insurance column does not move.
• Relief at source. The employer takes the contribution after tax and National Insurance, and the provider adds relief at the basic rate of 20% to the pot: £350 here. The payslip shows only your own contribution.

The student loan plan on the payroll

Each plan has its own threshold. On £35,000, Plan 5 repays £900 a year and Plan 2 repays £505, so an employer holding the wrong plan takes the wrong amount. Payroll also tests each payslip against a weekly or monthly threshold: a bonus can trigger a repayment in one month even when the year's pay ends up under the annual threshold, and gov.uk says a refund can then be requested after the tax year ends.

Benefits in kind

Company benefits such as cars, accommodation and loans are taxed, and the employer collects that tax from wages through PAYE. One route is the tax code: the value of the benefit comes off the allowance. The calculator does not model benefits, but a code can stand in for one. A £2,000 benefit turns 1257L into 1057L, and income tax on £35,000 rises from £4,486 to £4,886.

A part year

The calculator assumes the salary is paid for the whole tax year, 6 April 2026 to 5 April 2027. Six months at £35,000 is £17,500 of pay in the year, and the income tax on that is £986, not half of the full-year £4,486, because the £12,570 allowance is an amount for the year. How that reaches each payslip depends on the code. On an ordinary code tax follows income so far in the tax year. On an emergency code each payslip stands alone, and gov.uk says tax overpaid that way can be refunded.

The £35,000 salary page has the full-year ledger these comparisons start from.