Start with the salary, not the tax code
The calculator asks for salary before Income Tax and National Insurance. That figure is treated as the income the bands see. A tax code on a coding notice can give more or less than the standard Personal Allowance, including a Blind Person's Allowance or an underpayment collected through the code. None of that is on the form. Pension contributions are also left out, and the direction matters. Salary sacrifice reduces the pay that National Insurance sees. An employee contribution under relief at source does not. Gift Aid and the Marriage Allowance can change the tax bill on a return. They are not typed here, so a person who uses them will not see that relief in the result.
Wales can set Welsh rates of Income Tax. The GOV.UK page used for this guide publishes the main UK table, and the calculator follows that table rather than inventing a second set of Welsh bands. Scotland has its own Income Tax bands. Those bands are not stored. National Insurance for a category A employee is still the UK-wide charge, so the National Insurance half of a Scottish salary can be read from this page while the Income Tax half cannot. Two jobs, tips that are not in the salary, benefits in kind, and a director's annual earnings period are outside the sum. The result is the arithmetic of the published bands on one salary.
Personal Allowance and the three tax rates
The standard Personal Allowance on GOV.UK is £12,570. That slice is taxed at nothing. Above £100,000 of income the allowance falls by £1 for every £2. The calculator counts that in whole pounds, so £100,001 still has the full allowance and £100,002 loses £1. The allowance is zero once income reaches £125,140, which is £100,000 plus twice £12,570. GOV.UK describes the taper as applying to adjusted net income. Because pension and Gift Aid are not on the form, the typed salary is the income the taper sees.
With a full allowance, the basic rate of 20 percent runs from £12,571 to £50,270. That is a band of £37,700 of taxable income. The higher rate of 40 percent then runs up to £125,140, and the additional rate of 45 percent applies above that. GOV.UK also publishes the same ladder measured on taxable income after the allowance has been removed. The additional-rate threshold on that view is taxable income over £125,140. The two descriptions meet when the allowance has been tapered away: at £125,140 of income the allowance is zero, taxable income is £125,140, and the next pound is at 45 percent.
The tax on exactly £30,000, which sits entirely in the basic-rate band, is £3,486. The tax on exactly £125,140 is £42,516. The tax on £160,000 is £58,203. Those three results are the checks locked to the Income Tax function. They are annual figures. The pay frequency you pick does not change Income Tax. It changes National Insurance, because National Insurance uses the monthly or weekly thresholds GOV.UK publishes, and those thresholds are not a perfect fifty-two-week split of the year.
Employee National Insurance, category A
For 2026-27 a category A employee pays nothing up to the primary threshold, 8 percent up to the upper earnings limit, and 2 percent above that. The weekly figures on GOV.UK are £242 and £967. The monthly figures are £1,048 and £4,189. The category letter page works an example that this site reproduces: £1,000 in a week is nothing on the first £242, 8 percent of the next £725, which is £58, and 2 percent of the remaining £33, which is £0.66. The week comes to £58.66.
The yearly National Insurance line is that period amount, rounded to the penny, times 12 or times 52. On a salary of £30,000 paid monthly, employee National Insurance is £1,393.92. Twelve times a monthly calculation is not the same number as fifty-two times a weekly one, because the published monthly thresholds are not exactly the weekly ones times fifty-two over twelve. Pick the frequency that matches the payslip. Category letters other than A, including the married women's reduced rate and the deferment letters, are not applied.
Employer National Insurance is a different person's bill. For category A in 2026-27 the employer rate is 15 percent above the secondary threshold, which is £96 a week or £417 a month. The calculator shows that amount and does not subtract it from take-home pay. Someone with two jobs can have National Insurance worked out on each job, and the annual totals will not match a single salary of the same size.
What is left, including a student loan
Take-home pay is the salary minus Income Tax, minus employee National Insurance, minus the student-loan line. On £30,000 paid monthly, with no student loan, that is £30,000 minus £3,486 minus £1,393.92, which is £25,120.08. The student-loan line uses the same 2026-27 thresholds as the student-loan calculator. Plan 1, Plan 2, Plan 4 and Plan 5 are 9 percent of pay over the plan threshold. A postgraduate loan is 6 percent and can sit on top of one undergraduate plan. Payroll rounds each deduction down to the nearest pound for the week or the month, and the yearly figure is that pound amount times the number of periods.
Two undergraduate plans are not charged at 18 percent. The form allows one undergraduate plan plus a postgraduate loan. A bonus month can trigger a deduction even when the year ends under the annual threshold. Interest on the loan is not calculated. The loan guide compares Plan 2 with Plan 5, which is the pair people most often mix up because Plan 5 has the lower threshold and therefore starts sooner.
Statutory maternity pay and statutory sick pay are different payments, with their own GOV.UK rates, and they are not folded into this salary. If the year includes those payments, this page is the ordinary salary only. Use the maternity and sick-pay calculators for those weeks, and do not add the employer National Insurance figure to the employee's deduction. The number to take away is the one on the take-home line: tax, employee National Insurance, and any loan, each named separately so a payslip can be compared one line at a time.