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Tax bands are slices, not cliffs
A common mistake is to read a tax threshold as if one extra pound moves the whole salary to a new rate. It does not. The UK system applies different rates to different slices of taxable income. That is why a pay rise above £50,270 can still increase take-home pay even though part of the extra income may be taxed at 40% under standard England, Wales and Northern Ireland rules.
The first step is to separate gross income from taxable income. The standard Personal Allowance is £12,570 for 2026/27, but the amount available to you can differ because of income level, tax-code adjustments or other circumstances. After allowances, the remaining taxable income is allocated to the relevant bands.
2026/27
The standard England, Wales and Northern Ireland picture
For someone entitled to the full standard Personal Allowance, GOV.UK lists 20% basic-rate tax from £12,571 to £50,270, 40% higher-rate tax from £50,271 to £125,140 and 45% additional-rate tax above £125,140. The calculation is progressive: each rate applies to the part of taxable income that reaches that band.
TaxDecod’s default salary pages use the standard 1257L-style allowance assumption for England, Wales and Northern Ireland unless you select a different region or deduction setup. The result is an estimate, not a replacement for your actual HMRC tax code or payroll record.
High income
£100,000 is a different kind of threshold
Above £100,000 of adjusted net income, the Personal Allowance is reduced by £1 for every £2 above the limit. It can be fully withdrawn by £125,140. This is why people around that range can face a much higher effective marginal tax rate than the headline 40% band alone suggests.
If your income is near this range, adjusted net income matters more than headline salary alone. Pension contributions and Gift Aid can affect adjusted net income in specific circumstances, so high-income planning should use your real figures rather than a generic salary estimate.
Payroll
PAYE is the collection mechanism
Most employees do not manually pay Income Tax each month. Their employer uses PAYE and a tax code to work out how much tax to deduct from each pay packet. The tax code can reflect more than the standard allowance, so two people with the same annual salary can see different tax deductions.
When a salary calculator and a payslip disagree, check the tax code, pay frequency, year-to-date figures, taxable benefits, bonus or overtime payments and whether an emergency code is being used. These details often explain the difference better than the annual salary alone.