About Dollars Lab
Dollars Lab publishes free personal finance calculators that explain their own maths. Most calculators online hand you a number and stop there. These show the formula, the assumptions behind it, and a year-by-year breakdown you can inspect — so you can check the result rather than trust it.
There are currently 26 calculators covering saving, retirement, debt, cars, property, budgeting, and business.
How the calculators are built
Every tool uses standard, published financial formulas — amortisation, compound growth, present and future value. Nothing here is proprietary, and the article on each page explains the formula so you can verify it independently or reproduce it in a spreadsheet.
Where a calculation requires an assumption, it is stated on the page rather than buried. Where a common rule of thumb is genuinely contested — the 4% safe withdrawal rate, for example — the disagreement is explained instead of presenting one number as settled fact.
Every worked example in the articles is checked against a separate implementation of the formula before publication, and re-checked whenever a calculator's default inputs change.
What this site does not do
No personalised financial advice. These are educational tools that compute what you ask them to compute. Nothing here accounts for your full circumstances, and nothing here is a recommendation to take or avoid any particular action.
No specific product recommendations either. You will not find suggestions to use a particular bank, fund, broker, or lender, because that is where most finance sites quietly become advertising.
For decisions about your own money, a licensed financial adviser, accountant, or tax professional can consider things a calculator cannot. See our Terms of Use for the full disclaimer.
Your data
Every calculation runs entirely in your browser. The figures you type — your income, your debts, your balances — are never transmitted to us and never stored anywhere. There is no account, no email capture, and no logging of your inputs.
You can verify this: disconnect from the internet after a calculator page loads and it will keep working. Full details are in our Privacy Policy.
How this site makes money
Dollars Lab is funded by display advertising served through Google AdSense. We do not accept sponsored posts, we do not use affiliate links, and no advertiser has any influence over the content or the numbers a calculator produces.
Ads are kept out of the calculator area itself. You should never have to navigate around an advertisement to reach an input field.
Corrections
If you find an error in a calculation or an explanation, please report it through our contact form. Corrections to the underlying maths take priority over everything else, and we would rather fix a mistake than defend it.
Questions, suggestions for new calculators, and accessibility problems are all welcome there too — the contact page sets out what we can and cannot help with.