My Calculator Stack
Calculators with formulas and explanations.
Converters, math, fitness, finance, physics, and more — with the equations shown.
Featured
Age Calculator
Calculate age in years, months, and days from a birth date.
Open tool →Average Calculator
Compute the arithmetic mean of a list of numbers.
Open tool →BMI Calculator
Body mass index from weight and height (Metric or US units).
Open tool →Free Fall Calculator
Distance and impact speed for free fall from rest: s = ½ g t², v = g t.
Open tool →Future Value Calculator
Project how a present amount grows at a periodic rate.
Open tool →Percentage Calculator
Find a percent of a number, reverse percentages, and percent change.
Open tool →Scientific Calculator
Keyboard-first scientific calculator with DEG/RAD trig, 2nd functions, memory, history, and display modes.
Open tool →Tip Calculator
Calculate tip amount and total bill from a tip percentage.
Open tool →Unit Converter
Convert length, mass, temperature, area, volume, energy, and more.
Open tool →Browse by category
Indexable hubs with crawlable links to every tool in the family.
- Business calculators
- Chemistry calculators
- Construction calculators
- Converters calculators
- Cooking calculators
- Cryptography calculators
- Date Time calculators
- Design calculators
- Education calculators
- Encoding calculators
- Everyday calculators
- Finance calculators
- Fitness calculators
- Geometry calculators
- Home calculators
- Math calculators
- Other calculators
- Personal Finance calculators
- Physics calculators
- Sales calculators
- Statistics calculators
- Time calculators
- Travel calculators
- Units calculators
- Weather calculators
Learn the math
Short tutorials that unpack the formulas behind each tool.
How to Calculate BMI
Body mass index (BMI) is a screening ratio: body mass divided by the square of height. This tutorial walks through the SI formula, a 70 kg / 1.75 m worked example, and WHO adult category bands you can try with sliders. BMI is not a diagnosis of health, body fat, or disease.
Read tutorial → Fitness · 5 minHow to Calculate BMR
Basal metabolic rate (BMR) estimates the calories your body uses at rest. This tutorial walks through the Mifflin–St Jeor formulas, a 70 kg / 175 cm / age 30 worked example, and a playground that substitutes your numbers. BMR is an estimate of resting energy, not a meal plan or a medical assessment.
Read tutorial → Personal Finance · 5 minHow to Calculate Compound Interest
Compound interest reinvests earned interest into the balance, so later periods earn interest on interest. This tutorial walks through A = P(1 + r/m)^{mt}, a $5,000 / 4% / 10-year monthly worked example, and a playground that compares compound growth with simple interest. Figures are illustrative; fees and taxes are omitted.
Read tutorial → Math · 5 minHow to Calculate a Percentage
A percentage compares a part to a whole on a scale of 100. This tutorial walks through the three problems the Percentage Calculator solves: what is P% of X, X as a percent of Y, and percent change from A to B. The worked example uses the same 15% of 80 defaults as the calculator.
Read tutorial →Formula sheets
Printable one-pagers — key formulas at a glance.
Elapsed Time & Lap Splits
Core stopwatch identities: elapsed difference, paused totals, and lap splits at a glance.
Open sheet → UnitsUnit Conversion Factor Labels
Dimensional-analysis cheatsheet: convert through a base unit, cancel labels, and handle temperature offsets.
Open sheet → MathPercentage Triad
Three rearrangements of part, whole, and rate — plus percent change for growth and decline.
Open sheet → FitnessAdult BMI
Metric BMI identity, US customary conversion, and WHO adult category cutoffs used as a screening ratio — not a diagnosis.
Open sheet → OtherGPA and Weighted Grades
Letter-to-points on a 4.0 scale, credit-hour GPA, and a weighted course average from score × weight pairs.
Open sheet →