How TaxDue calculates an estimate.

Editorial responsibility and independence

TaxDue’s operator is responsible for the calculator code, explanatory copy, source selection and corrections. No government department, tax authority, platform or named third party reviews, approves or endorses TaxDue. A link to a source means that the page supports a rule used or a limitation described; it does not transfer responsibility for our calculation to the publisher.

The service does not claim a professional tax-adviser review. Automated checks and source comparisons reduce avoidable errors, but they cannot replace an accountant, solicitor, tax adviser or financial adviser who has the user’s complete facts. Pages say what is omitted so a narrow estimate is not mistaken for a complete tax computation.

Sources and hierarchy

We prefer legislation-backed guidance and official rate tables. Each calculator links to the sources most relevant to its result. Where official guidance leaves a practical ambiguity, the calculator uses a conservative, visible assumption or declines to show a result.

• Income Tax rates and allowances · GOV.UK
• Scottish Income Tax factsheet · Scottish Government
• Employer rates and thresholds · HMRC
• Land and Buildings Transaction Tax · Revenue Scotland
• Land Transaction Tax · Welsh Revenue Authority

Annual and monthly figures

Recurring income and costs can be entered monthly or annually. Monthly entries are multiplied by 12 for the annual calculation, and annual entries are divided by 12 for the displayed monthly equivalent. A monthly tax reserve spreads the annual estimate evenly across 12 months; it does not mean HMRC collects tax monthly.

One-off taxes such as property transaction tax, Capital Gains Tax and Inheritance Tax are shown as totals with the relevant reporting or payment timetable where the calculator can identify it.

UK regions

Scottish Income Tax bands apply when Scotland is selected. England, Wales and Northern Ireland share the non-savings, non-dividend Income Tax bands used in the other option. Dividend rates and National Insurance remain UK-wide in these tools. Property purchase tax is separated into SDLT for England and Northern Ireland, LBTT for Scotland and LTT for Wales.

Pension treatment

Salary sacrifice, net pay arrangements and relief at source affect taxable pay differently, so calculators identify the method they use. The annual-allowance calculator separates money-purchase input from defined-benefit and other input. When the Money Purchase Annual Allowance applies, carry forward never increases the £10,000 money-purchase limit; it can be relevant to the alternative allowance for other pension input.

Rounding and presentation

Calculations use unrounded values internally unless the statutory rule calls for rounding. Most totals are then displayed to the nearest pound for readability; VAT keeps pence. Payroll can differ because employers calculate by pay period and apply statutory rounding at different stages.

Quality checks

The current automated suite contains 139 statutory and boundary assertions covering rates, allowances, tax-band transitions, devolved property taxes, National Insurance, student loans, pension taper and MPAA cases, Child Benefit partner selection, K-code limits and invalid tax codes. We also check every indexable page for a unique title, description, canonical URL, social preview, structured data, sitemap presence and crawlability.

Inputs that cannot sensibly coexist—such as VAT above an invoice, a home worth more than the estate, or company extraction above available profit—stop the result and explain what needs correcting.

A review date means the listed sources and test cases were checked on that date. It does not mean an authority or professional adviser certified the page. When a credible error is reported, we reproduce it, compare the result with the governing source, correct code and copy together, and add a regression test where the issue can be expressed as a boundary or example.

Change log

Report a possible error

If a result looks wrong, stop relying on it and email legal@taxdue.org. Include the calculator URL, the figures needed to reproduce the issue and the official source you believe applies. Do not include a tax return, National Insurance number, bank details or other sensitive records.