About CentExact

CentExact is a small, independent set of free personal finance calculators covering borrowing, saving, pay, tax and selling online. The goal is simple: give you the number you came for, and show enough of the working that you can check it.

How the calculators are built

Every calculator starts with the published formula: the amortisation equation a lender uses, the tax bands a revenue authority publishes, the CPI series a statistics office releases. That formula is implemented once, as a pure function, and pinned with automated tests against reference values: spreadsheet results, worked examples from official guidance, and figures from the institutions themselves.

Where a calculation depends on data that changes (tax thresholds, fee schedules, price indices), the data is stored separately from the code with its source, the date it took effect and the date we retrieved it. That provenance is shown on the page under Data sources, together with a freshness indicator, so you can see at a glance whether a table is current.

Schedules are built the way a bank builds them: the payment and each period's interest are rounded to the cent, and the final payment settles the exact balance. That is why our totals can differ from a spreadsheet formula by a few cents, and why we show both figures.

What CentExact is not

CentExact is not a financial adviser, lender, tax agent or medical professional, and nothing here is advice. A calculator can tell you what a formula produces from the numbers you enter; it cannot know your circumstances. Check any decision that matters with the institution involved or a qualified professional.

Funding

CentExact is free to use and is funded by advertising. Ads are clearly labelled, appear in fixed positions that never move the content around, and are never placed inside a calculator's inputs or results. We do not sell your data and we do not run sponsored calculators. See the privacy policy for details of what is collected.

Corrections

If you find an error (a wrong figure, an out-of-date threshold, a formula that does not match your lender's statement), please tell us. Reports are checked against the source, fixed, and the review date on the page is updated.