Methodology

The calculators use programmed rules and a selected set of tax-year rates. The same inputs and tax-year settings produce the same result. AI does not generate the tax or take-home figures.

Automated checks compare results with reference examples calculated from published tax bands, cover thresholds and pension methods, and check that changes do not alter stored examples for earlier tax years. Further tests check relationships such as gross pay minus deductions equalling net pay.

Passing these tests provides evidence about the cases covered. It is not HMRC certification, an independent professional audit, or a guarantee that every employer-specific payroll arrangement is reproduced.

Real Offer Net reuses the salary engine, subtracts annual commute costs, and divides remaining cash by working and travelling hours. Default working weeks are 46.4, editable for your working pattern. Effective hourly pay is not a minimum-wage check.

Your Real Pay uses the ONS annual all-items CPI rate (D7G7), checked against the D7BT index. Purchasing power is current pay divided by the price factor; inflation-matching pay is previous pay multiplied by that factor. Without previous pay, the comparison explicitly assumes unchanged pay. Gross mode does not calculate disposable income.

Tax Cliffs Map shows thresholds and effective marginal rates using the selected tax-year settings. Adjusted net income positions allowance and Child Benefit markers; employee NI uses salary. It does not calculate a full take-home breakdown. CPI snapshots are dated and archived; updates must pass source and integrity checks before publication.

IsMyPayRight uses HMRC-based rules and published rates for income tax, employee and employer National Insurance, student loans, marriage allowance, and the main allowance rules that affect PAYE outcomes.

The engine calculates annual figures first and then derives monthly, weekly, and other frequency views from that annual result. Tax-year logic lives in explicit tax-year configuration files rather than being hard-coded into the UI.

The current public calculator supports the tax years available in the engine and applies the region you select. Scotland uses Scottish income-tax bands. England, Wales, and Northern Ireland use the main UK income-tax bands. National Insurance follows the UK-wide thresholds for the relevant tax year.

Where HMRC rules differ by tax year, the calculator uses the selected year rather than trying to back-fit current thresholds onto older scenarios.

The payslip checker compares the values you enter against an HMRC-based estimate for the selected tax year, pay frequency, tax code, region, and student-loan plan. It flags differences to review and explains the path from gross pay to net pay. A difference is not confirmation that payroll is wrong.

More complex payslips can include salary sacrifice, taxable benefits, and other deductions. In the checker these are grouped into practical buckets rather than trying to recreate every payroll provider layout line by line.

Salary sacrifice is modelled directly inside the calculator rather than as a separate side tool. The calculator currently supports Cycle to Work, Holiday Buy, EV salary sacrifice, and pension increase scenarios.

Holiday Buy is estimated from the annual amount or extra days entered. EV car tax uses the P11D list price and selected year’s zero-emission percentage, including tax-band crossings and the Personal Allowance taper. It assumes full-year availability and no employee capital/private-use payments. Missing P11D values produce a warning and exclude car tax; codes must not already collect that car benefit.

The reverse calculator solves for the gross salary needed to reach a target net figure using the same PAYE engine as the forward calculator. Monthly targets are annualised before the reverse calculation is solved.

The two-jobs calculator treats each employment separately for PAYE and National Insurance, then combines the results. It also highlights where multiple employments can change NI outcomes and whether annual-maximum overpayment rules may be relevant.

Payslip upload is optional. If you upload an image or PDF, Google Gemini, an AI service, attempts to read the fields. You review and correct those values before using them in a calculation. Manual entry is also available.

Extraction is not treated as a final answer or a professional review. An unclear, unusually formatted, or cropped payslip can produce missing or incorrect fields. IsMyPayRight does not retain the uploaded file after extraction; the privacy notice explains processing and sharing in more detail.

Results are designed to be transparent and useful, but they are still estimates. Real payroll outcomes can differ because of employer-specific setups, cumulative basis (meaning your tax is spread across the whole year, not calculated fresh each month) versus non-cumulative treatment, mid-period changes, court-ordered deductions (such as attachment of earnings), provider-specific salary-sacrifice rules, or payroll corrections already in flight.

Net pay pension arrangements reduce income tax but leave NI and student loan pay unchanged. Relief-at-source estimates include the provider’s 20% relief and use gross contributions for allowance restoration, but exclude separately claimed relief above 20%. Pension deductions are entered amounts, not a check of scheme entitlement. Date-range pro-rata results show gross pay only: annual deductions cannot establish short-period take-home. Statutory pay checks the earnings test only, assumes salary divided by 52 and weekly NI, excludes pensions and uses weekly student-loan deductions, and groups budgets into four-week blocks. Mortgage thresholds and stress rates are planning assumptions, not lending criteria. The two-payslip comparison compares entered amounts locally and highlights changes and unreconciled totals; it does not infer a confirmed cause. The checker is not a payroll audit, the payslip display is not an employer-produced payslip, and EV modelling is intentionally simplified. If an important financial decision depends on a result, verify it against your employer payroll, payslip, P60, or HMRC account.