The formula, the source,
and the date.
Kit Space is a free library of online calculators — finance, business, lifestyle, legal, environment and gaming. Every guide states the formula it uses, names the source behind any external figure, and shows when it was last reviewed. Check the arithmetic yourself instead of trusting a black box.
A calculator is only
as good as its sources.
There are thousands of calculator sites on the internet. Most of them hide the formula, quote a number with no date on it, and hope you will not check.
Kit Space is built the other way round. Each calculator prints the equation it uses. Where a tool depends on a figure set by someone else — a tax bracket, a statutory limit, an emissions factor, a food-safety time — the page names that source and says when it was last checked.
What can you calculate?
Every calculator runs in your browser. Nothing to install, nothing to sign up for.
Finance
Tax, retirement and investment arithmetic, loan and interest schedules, business valuation and personal balance-sheet maths. Examples: 1099 Tax, After-Fee Return, Annuity Payment.
See the Finance tools →Business & Trade
Unit economics, pricing and elasticity, marketing and funnel metrics, payroll and staffing ratios, inventory and trade costs. Examples: Affiliate Commission, ARR (Annual Recurring Revenue), Attendance Rate.
See the Business & Trade tools →Lifestyle
Cooking, baking and preserving ratios, household and budget planning, pet and family timelines, craft and hobby projects. Examples: Anniversary, Baking Temperature, Bread Hydration.
See the Lifestyle tools →Legal
Cost estimators for common legal processes, compliance and record-keeping obligations, estate and executor arithmetic. Examples: Age of Majority, Annulment Eligibility, Arbitration Cost Estimator.
See the Legal tools →Environment
Carbon accounting, transport and energy comparisons, waste and recycling maths, sustainability programme costing. Examples: Animal Agriculture Water Footprint, Bicycle vs Car Emissions, Bird Migration Climate Impact.
See the Environment tools →Gaming
Drop rates and draw probability, build and gear optimisation, progression and ranking models. Examples: Battleground Rating, Card Draw Probability, Clan Donation Efficiency.
See the Gaming tools →Browse calculators
A selection from the full library. Filter by category, or see the complete list.
Written guides
Some questions need more than a number. These guides walk through the metric, the arithmetic and a worked example you can follow on paper. See all guides →
Kit Space is edited by Owen Renshaw
Kit Space is an independent publication. One editor writes the guides, builds and reviews the calculators, and answers the corrections inbox. There is no editorial board behind the byline and no outsourced content desk.
We publish the arithmetic and the assumptions behind it. We do not publish advice: Kit Space is not an advisory service, and nothing here is tailored to your circumstances. Where a decision matters, take it to a qualified professional in your own jurisdiction.
Frequently asked questions
Straight answers about how Kit Space works.
Find the number you need
Free calculators, no sign-up, no cost.
Explore all toolsKit Space publishes calculations, not advice. Results depend on the figures you enter, and reference values change. Please read the Disclaimer before you rely on any output.