How we build and check our tools

The formulas

Every calculator uses the standard definition from accounting and finance practice: margin as a share of price, markup as a share of cost, loan payments by the standard amortisation formula, and so on. Each tool page shows its formula in plain words next to the result, so you can check any answer by hand.

How we test

• Worked examples are checked by hand. The example on every tool page is recalculated independently before publishing, and the tool must give the same answer.
• Every tool is stress-tested on each release. An automated test opens every tool, tries every option and enters awkward values such as zero, negative numbers, very large numbers, letters and empty fields. A release fails if any tool shows an error or a meaningless result.
• Documents are print-tested. Invoices, receipts, quotes and the other document makers are checked to print and save as PDF with only the document on the page.

Rates from other companies and governments

Some tools are pre-filled with figures set by others, such as marketplace and payment fees, shipping divisors and tax rates. We take these from the provider's or government's own published pages, show the month we checked them next to the figure, and let you change every one. They change without notice, so always confirm them for your country, plan and account.

What our tools do not do

Results are estimates for planning and general information. They are not financial, tax, payroll or legal advice, and they cannot know your full circumstances. For decisions with legal or tax consequences, check with a qualified accountant or adviser. Read the full disclaimer.

Reviews and dates

Each tool page shows when it was last reviewed. We review tools when rules or published rates change, and when someone reports a problem.

Independence

Tallyvane is paid for by ads and clearly labelled partner links. Advertisers and partners have no say in how a tool calculates or what its guidance says. See our affiliate disclosure.

Report a mistake

If a result looks wrong, email [email protected] with the tool, the numbers you entered and the result you expected. We check every report and correct confirmed mistakes as a priority.