Free tools
Why these are free and open
A calculator is a small, self-contained question: what does this number become under these assumptions? Charging for the answer, or requiring an account to see it, puts a wall in front of the part that takes one line of arithmetic. So the arithmetic lives here, runs entirely in your browser, and never leaves it.
The apps are for the part that outgrows a calculator: keeping a plan between visits, with many named records rather than one scratch space. Budgettin holds the categories, the transactions and the receipts; Matrix Calc keeps named matrices you can come back to. Both are linked from each tool, and neither is required to use it.
A note on the numbers
These tools are planning estimates. A lender quotes a rate with its own fees, a savings account changes its rate, and tax rules differ by country. Use the result to compare options and ask better questions — not as a contract.
Each tool shows the formula it used and a worked example with real numbers, so the answer can be checked rather than trusted.
How each one is checked
Every tool page prints the formula it applies, works an example through it with real figures, and names the primary reference the explanation was checked against — a standard derivation, a regulator's guidance, a reference implementation — with the date it was last checked. The arithmetic itself is covered by a test runner, so a change to a calculator that moves a result fails before it ships.
The four tools are also where the site's corrections show up first: a wrong figure or a stale source is fixed on the page and dated in the changelog, rather than quietly dropped.
Questions people ask
- Do I need an account to use these tools?
- No. Every calculator runs in your browser and sends nothing to a server, so there is no sign-up, no email and no limit on how often you use it. The money calculators keep nothing — closing the tab discards their inputs. The matrix calculator saves its workspace in this browser so it reopens where you left it; clearing site data clears that too.
- How accurate are the results?
- Each tool shows the formula it applied and a worked example, so the arithmetic can be checked. The inputs are yours, though: a lender adds fees, a savings rate changes, and tax rules differ by country, so treat a result as a planning estimate rather than a quote.
- What is the difference between a tool and the apps?
- A tool answers one question at a time. The apps keep the plan between visits: Budgettin holds your categories, transactions and receipts so the budget recalculates itself, and Matrix Calc keeps named matrices you want to come back to. Neither is needed to use the free tools.