Calculation method

Tax year and scope

The calculator uses England’s rates and thresholds for 2026-04-06 to 2027-04-05. Sources are listed below.

An annual estimate

Gross salary is the only income. The model applies the standard Personal Allowance, its taper, England's income tax bands and annual employee NI thresholds. It assumes an ordinary employee below State Pension age. Selected pension contributions and student/postgraduate loans are included. Directors, special tax codes, part-year work, other income, additional allowances and pension annual-allowance tax charges are excluded. Loan amounts use annual thresholds without modelling final balances or payroll whole-pound rounding. Relief-at-source take-home excludes extra relief not yet claimed; the potential additional relief is shown separately.

Rounding

We use integer pence and preserve half-pennies during the allowance taper. Each total deduction is rounded to the nearest penny, with halves rounded up. Monthly and weekly figures divide annual take-home by 12 and 52 and round for display. Displayed workings are rounded to pennies; the calculation retains half-pennies during taper, so displayed intermediate amounts can differ slightly from exact arithmetic. This is an estimate convention, not an implementation of HMRC payroll rounding.

Other calculators

The student loan, pension, salary sacrifice and part-time tools use the same tax and deduction rules. The Child Benefit tool applies the charge to the higher adjusted net income and uses statutory whole-pound rounding. Mortgage affordability uses constant-rate monthly amortisation, an editable income multiple and your entered household budget. The wider directory includes savings and residential property taxes, employment entitlements and scenario models for investments, loans and energy. Projections assume the rates and timescales entered; they do not predict returns or recommend products. Each tool lists its supported cases, formula and limitations.

Testing and review

Automated tests cover tax thresholds, the Personal Allowance taper, pensions, loan deductions and worked examples. A separate AI-assisted review recomputed the tax and benefit examples from official rates, verified the ONS benchmarks and checked the mortgage formula independently. Checks against HMRC’s own calculators are still pending. These checks are not professional tax accreditation.

Sources

• Personal Allowance and adjusted-net-income taper
• Category A rates and annual NI thresholds
• NI normally deducted per pay period
• Separate employment NI liabilities and aggregation exceptions
• Plan thresholds, rates and simultaneous undergraduate/postgraduate deductions
• Loan earnings follow Class 1 NI earnings; pension net pay does not lower loan earnings
• Multiple employers and Self Assessment loan aggregation
• Voluntary repayments may not help before write-off and are not refundable
• Net pay and relief-at-source treatment, 20% provider relief and additional relief limited to higher-taxed income
• Pension salary sacrifice reduces cash pay and NI earnings; minimum-wage restriction
• Gross relief-at-source contributions reduce adjusted net income
• Standard annual allowance includes employer contributions; taper/MPAA may apply
• Section 10(6): relief-at-source extension of basic and higher-rate limits under Finance Act 2004 s192(4)

Sources checked 2026-10-25.

Read the dated rules file (JSON) · Use the calculator

Corrections

Email hello@sumsavvy.co.uk with the tax year and a description of the issue. Do not send payslips, National Insurance numbers or other sensitive information. Read the change history.