Where the rules come from
We work from primary sources: GOV.UK, HMRC’s guidance and internal manuals, the legislation itself, the FCA’s Handbook, and the bodies that run the systems our tools check against. Lenders’ and card providers’ published examples are used only to test our figures.
| Tool | Source | Last checked |
|---|---|---|
| IBAN checker | SWIFT IBAN Registry, release of 15 September 2026 (ISO 13616) | 4 October 2026 |
| Invoice generator | GOV.UK, what an invoice must include; HMRC VAT Notice 700/21; VAT Notice 700 paragraph 17.5; HMRC manuals VATREC12010 and VATREVCON37100 | 4 October 2026 |
| Corporation tax calculator | GOV.UK, corporation tax rates and allowances, marginal relief, and paying in instalments; Finance Act 2026, sections 11 and 12; HMRC manuals CTM01800, CTM03925, CTM03955, CTM03956, CTM92520 and CTM92530; Corporation Tax Act 2010, section 18D | 5 October 2026 |
| Dividend tax calculator | GOV.UK, income tax rates and allowances, tax on dividends, Scottish income tax, rates and thresholds for employers 2026 to 2027, and Employment Allowance for single-director companies; gov.scot, Scottish income tax rates and bands 2026 to 2027; Finance Act 2026, section 4; Income Tax Act 2007, sections 13, 16 and 25 | 5 October 2026 |
| Salary sacrifice calculator | GOV.UK, rates and thresholds for employers 2026 to 2027, salary sacrifice and the effects on PAYE, student loan deduction tables, national minimum wage rates, and the High Income Child Benefit charge; HMRC manual EIM24705; Finance Act 2025, sections 5 and 6; HMRC, salary sacrifice reform from 6 April 2029; NICs (Employer Pensions Contributions) Act 2026, section 1; DfT, cycle to work scheme guidance | 5 October 2026 |
| Inheritance tax calculator | GOV.UK, inheritance tax thresholds, the residence nil-rate band, gifts and the 7-year rule, leaving to charity, and business and agricultural relief; Finance Act 2026, sections 66 and 72; HMRC manuals IHTM14143, IHTM14612, IHTM45010 and IHTM46023; HMRC’s technical note on inheritance tax on pensions | 5 October 2026 |
| Loan repayment calculator | FCA Handbook, CONC App 1.2.6R (the APR) and CONC 3.5 (representative APR); Consumer Credit Act 1974, sections 94 and 95A; Consumer Credit (Early Settlement) Regulations 2004, regulations 4 to 6; MoneyHelper, personal loans | 6 October 2026 |
| Credit card repayment calculator | FCA Handbook, CONC 6.7 (minimum payments and persistent debt); card providers’ published minimum payment rules; MoneyHelper, balance transfers and persistent debt; Bank of England, Money and Credit, August 2026 | 6 October 2026 |
| PCP car finance calculator | Consumer Credit Act 1974, sections 99, 100 and 189; Consumer Credit (Early Settlement) Regulations 2004, regulations 4 to 6; MoneyHelper, personal contract purchase; FCA, car finance complaints | 6 October 2026 |
How each tool is tested
Before we build a tool, we write down its rules and a set of test cases: the inputs and the answers the rules must give, taken from official worked examples wherever they exist. Every calculation and check is then tested against those cases, plus awkward inputs such as blank fields, pasted symbols and very large numbers. If a single test fails, the change can’t be published.
Tools that ask an official service, such as the VAT number checker, are tested against that service’s own test system before they go live.
Review before it goes live
A chartered management accountant reviews each tool’s rules, workings and wording before it is published, and again after each Budget and each April. You can read more about him on the About page. We never say a page has been reviewed when it hasn’t.
What “last checked” means
The small print at the end of each tool says which rules it follows and when we last confirmed those rules against the source. If a source changes between checks, we update the tool and the date together.
When we update
- After each Budget, we check every tool affected by announced changes.
- Each April, before the new tax year starts on 6 April, we re-check every rate and threshold.
- When a source changes, such as a new SWIFT IBAN Registry release, we update the data and the date shown.
If you think something is out of date, please tell us.