81 calculators · 6 languages · sources on every page
Calculators that show the formula, not just the number
Enter your values, read the result straight away, then check how it was reached: the formula, a worked example, the limits of the method and the references used. Nothing here is estimated by an AI.
e.g. VAT, BMI, mortgage, percentage81 calculators
Formula on the page
6 languages
Français · English · Español · Português · Deutsch · العربية
12 families
Browse by category
Most requested
The tools visitors open first. Each one works without an account and without sending your inputs anywhere.
- MathematicsPercentageEnter two numbers of the same kind. The tool returns (part ÷ total) × 100 — useful for a test score, a slice of a budget, or a share of a count.
- FinanceSales tax / VATOne amount and one rate. The tool either adds tax (net → gross) or extracts it (gross → net) and shows the tax slice.
- Health and nutritionBMI calculatorBody mass index is weight in kg divided by height in meters squared. Labels use adult WHO cut-offs. That is not an obesity diagnosis by itself, and it is not a child BMI.
- FinanceMortgageCompute the amortizing monthly P&I (12 payments a year) and, if you want, a flat annual insurance amount spread over 12 months. This is not a loan offer. APR is not calculated.
- Health and nutritionCalorie calculatorThree steps: Mifflin-St Jeor resting burn, times a lump activity factor, then a goal offset. The result is an estimate, not a diet.
- Family and cycleOvulation calculatorOne date: the first day of the last period. The tool places ovulation on day 14 and a fertile window from day 10 to day 17.
- Strength and cardioOne-rep max (Epley)A load and a rep count (1 to 12). The tool applies Epley, not a true single-attempt max.
- Grades and studyGPA calculatorEnter a letter and credits per course. The GPA is the sum of grade points times credits, divided by total credits.
Browse by category
Twelve families of tools, from math to cooking. Each category explains what it covers and links across to closely related calculators.
Mathematics
16 toolsTools that give an exact result, then show the formula. Each page spells out edge cases (division by zero, impossible triangles, rounding).
Finance
14 toolsPayments, interest and returns: the formulas are amortization and compound interest. Fees, insurance and tax appear only if the form includes them.
Health and nutrition
10 toolsThese tools estimate an order of magnitude (energy expenditure, BMI, protein) from published formulas. They do not replace medical, dietetic or coaching advice.
Building and garden
5 toolsThe core math is a volume or an area. A waste margin (offcuts, redo, relief) is added because a site is not a perfect slab.
Unit converters
12 toolsEach conversion uses a factor fixed by SI or by a legal definition (inch, pound). Temperature goes through kelvin so the scales stay consistent.
Dates and durations
5 toolsDurations use civil UTC dates (year-month-day) to avoid daylight-saving shifts. A “day” here is a calendar date, not 24 astronomical hours.
Energy and vehicle
4 toolsThese tools turn a consumption figure and a unit price into money spent. They do not guess your driving or your tariff: they apply the numbers you enter.
Grades and study
7 toolsThese tools apply the grading rules your school set. They do not guess your scheme: you enter the weights, they do the arithmetic and show the working.
Family and cycle
2 toolsTwo calendars start from the same point: the first day of the last period. One places ovulation on day 14 of a 28-day cycle; the other counts weeks of amenorrhea and the trimester. They do not replace a urine test, an ultrasound or an appointment.
Pets
2 toolsThe “times seven” rule is wrong: the first two years count more, then the pace depends on the species and, for dogs, adult size. These pages apply a teaching chart and say so.
Cooking
2 toolsTwo frequent kitchen jobs: scale a recipe when guest count changes, and read bread-dough hydration. The first is a rule of three; the second is baker’s percentage. Neither returns a baking time.
Strength and cardio
2 toolsTwo training estimates: a one-rep max from a set of 1 to 12 reps (Epley), and five pulse zones from age and resting HR (Karvonen, max HR = 220 − age). Neither is a lab test.
How these calculators are built
01
The maths is tested, not generated
Every result comes from a unit-tested function. The same inputs always give the same number, and changing a formula requires a new test before it ships.
02
The method is written out
The formula, a worked example and the assumptions all sit on the page. You can redo the calculation by hand and land on the same answer.
03
The limits are stated, not buried
A BMI does not measure body fat, and a monthly payment is not an APR. When a tool cannot answer your question, the page says so.
Frequently asked questions
Are the calculators free?
Yes. Every tool is available with no account, no sign-up and no usage limit. The calculations run in your browser.
Is my data sent anywhere?
No. The values you type stay in your browser: they are never sent to a server and nothing is stored.
Can I rely on the health and finance results?
They are estimates from published formulas, with the sources and limits stated on each page. They do not replace a doctor, a dietitian or a financial adviser.
Which languages is the site available in?
French, English, Spanish, Portuguese, German and Arabic. Each language has its own pages, translated URLs and locally adapted examples.