All 100 Free Online Calculators

Not sure which tool you need?

Start from the question rather than the name. If you are asking what something will be worth later, you want the compound interest or future value calculator. If you are asking what something costs you, start with loan payment or credit card interest. If you are asking whether a price works, the profit margin and break-even tools are the pair to reach for, and the product pricing calculator solves the same relationship backwards.

Health questions chain together in a fixed order: BMR gives what you burn at rest, TDEE adds your activity, calories turns that into a goal, and macros splits the goal into grams. Construction questions almost all start with square footage, because area is the input every material calculation needs.

How the list is organised

The default order puts the twenty-one most-used calculators first and then follows the order they appear in our index, which groups them by subject. A – Z is the obvious alternative when you know the name. Newest reverses the index order, which surfaces the everyday and construction tools that were added last.

Category chips are additive rather than exclusive: select Finance and Mortgage together and you see all thirty of those tools at once, which is useful when a question straddles both. The count beside the chips updates live, so you can see how much a filter narrowed things before you scroll.

One habit that pays off: the filter box matches keywords as well as names. Several calculators are best found by the problem rather than the title — typing overtime finds the work hours calculator, deposit finds the down payment one, and macros finds the macro calculator even though the page is titled differently. If a search you would expect to work does not, that is a gap in our keywords and we would like to hear about it.

What every calculator here has in common

Whatever you open from this grid, the page is built the same way. There is a calculator card at the top that updates as you type, with sliders on the fields where dragging is faster than typing and unit toggles where two systems are in common use. Below it sits the result panel: one headline figure, two to four supporting numbers, and — where it helps — a chart or a full breakdown table.

Under that comes the writing: how to use the tool, the formula with every variable defined, at least one example worked through by hand, how to read the result, and where the method stops being reliable. That last section is the one we spend longest on, because a number without its caveats is worse than no number at all.

Every page also offers three things at the bottom of the result panel. Copy puts the inputs and the result on your clipboard as plain text. Share link builds a URL with your numbers in it, so a colleague opens the same calculation rather than a blank form. Print produces a clean one-page sheet with no navigation and no advertising on it.

Each of the nine category pages explains its own tools in more depth and says which one to choose when two look similar. If none of the hundred answers your question, email info@factonisam.com — a fair number of these started as a request.