A working library of financial, health, mathematical and everyday calculators. Enter a figure — the answer, the schedule and the chart update as you type.
Loans, mortgages, investing, tax and the arithmetic of long horizons.
Body composition, energy balance, pregnancy dates and training load.
Geometry, statistics, number theory and a full scientific keypad.
Dates, units, construction materials, grades and household sums.
Mr Calculator.org is a working reference library: every tool on this page runs the arithmetic the moment you type, so a repayment, a body measurement or a percentage is answered in place. There is nothing to install, no account to create and no page reload — enter your numbers and the answer, the schedule and the chart follow. Each calculator uses a standard published formula and shows the figures behind the result, so the working can be checked line by line instead of taken on trust.
Borrowing, saving and running a small business come down to the same handful of questions. Work out a monthly repayment and the interest it carries, see what a bond you can actually afford looks like next to one the bank might approve, and check how much of the payment is interest in the first year. Add VAT or sales tax, strip it back out of a gross figure, or follow a currency through a live exchange rate.
A few measurements — height, weight, waist, age, activity — are enough to sketch a useful picture. Body mass index sits beside waist-to-height and ideal-weight ranges so a single number is never the whole story. Basal metabolic rate and daily energy needs show what maintenance looks like, and the macronutrient split turns that into grams of protein, carbohydrate and fat. Pregnancy dating estimates a due date and the weeks that follow it.
The rest of the library covers the arithmetic that interrupts a normal day: percentage change on a price, a fraction that needs simplifying, area and volume before ordering materials, standard deviation across a set of scores, a quadratic that will not factorise. Away from the desk there is a tip split between any number of people, the days between two dates, a fuel cost for a trip, and a password strong enough to be worth keeping.