Online calculators
Percentages, discounts, margins, basic statistics and compound interest, with formula and example always visible.
Tools in this category
Percentages
Math
Rule of Three Calculator
Solves a direct or inverse rule of three.
Average Calculator
Calculates the average of a list of numbers.
Median Calculator
Calculates the median of a list of numbers.
LCM Calculator
Calculates the least common multiple.
GCD Calculator
Calculates the greatest common divisor.
Root Calculator
Square root or root of any index.
Logarithm Calculator
Common and natural logarithm.
Trigonometry Calculator
Sine, cosine, tangent, cosecant, secant and cotangent.
Degrees to Radians Converter
Converts angles between degrees and radians.
Finance
Margin Calculator
Calculates the profit margin.
Markup Calculator
Calculates the markup over cost.
VAT Calculator
Adds or removes VAT from an amount.
Compound Interest Calculator
Calculates compound interest growth.
Mortgage Calculator
Calculates a mortgage's monthly payment.
Loan Calculator
Calculates a loan's monthly payment.
Health
Physical quantities
Temperature Converter
Converts between Celsius, Fahrenheit, Kelvin and Rankine.
Length Converter
From light-years to ångströms via km, m and mm.
Metric to Imperial Length Converter
km, m and cm to inches, feet, yards and miles.
Mass Converter
From milligrams to metric tonnes.
Metric to Imperial Mass Converter
g, kg and t to ounces, pounds, stone and tons.
Area Converter
mm², m², ares, hectares and km².
Metric to Imperial Area Converter
m², ares and hectares to ft², acres and mi².
Volume Converter
mm³, cm³, litres, m³ and km³.
Metric to Imperial Volume Converter
Litres and m³ to US/UK gallons, pints, cups and ounces.
Time Unit Converter
Seconds, hours, days, years, centuries and eons.
Energy Converter
kWh, joules, calories, eV, ergs and more.
Force Converter
Newton, dyne, kilopond and pound-force.
Pressure Converter
Pascal, atmosphere, bar, mmHg and PSI.
Magnetic Unit Converter
Tesla ↔ gauss and weber ↔ maxwell.
Data Storage Converter
Bits, bytes, KB, MB, GB, TB… and KiB, MiB, GiB.
LED Bulb Equivalence
Actual LED watts vs equivalent incandescent watts.
"Calculating a percentage" can mean very different things: the percentage of an amount, how much a value has changed, or how interest compounds over time. This guide helps you identify which operation you need and what each calculator assumes.
Which kind of calculation you need
- Percentage of an amount: how much X% of a number is.
- Percentage change: how much a value went up or down compared to another, as a percentage.
- Business pricing: applying a discount, calculating margin or markup, adding or removing VAT.
- Growth and interest: compound interest, a mortgage or loan payment.
- Health: body mass index, daily calories, total energy expenditure.
- Statistics and math: average, median, GCD, LCM, rule of three.
Percentages: of an amount, change and difference
These are three different calculations that are often confused. The percentage of an amount multiplies the value by the percentage and divides by 100 (20% of 50 is 10). Percentage change compares a starting value to an ending one: (end − start) / start × 100, and the result can be negative if the value went down. Percentage difference is not the same as percentage change: it measures how far apart two values are from each other, using their average as the reference, so it's always positive and doesn't depend on which value is larger.
Pricing, discounts and business margins
Margin and markup are not the same thing, even though they're constantly mixed up. Margin is calculated on the sale price: (price − cost) / price. Markup is calculated on the cost: (price − cost) / cost. A 50% margin does not equal a 50% markup -- for the same cost and price, markup always comes out higher than margin. The discount calculator applies a percentage directly to an original price; the VAT calculator adds or removes a tax percentage from an amount, using whatever rate you enter (it does not automatically apply any country's legal rate).
Compound interest, mortgages and loans
Simple interest is always calculated on the original principal; compound interest is calculated on the principal plus interest already accumulated, which is why it grows faster the longer it runs. The compound interest calculator lets you add periodic contributions and choose how many times a year interest compounds. A mortgage or loan payment is a different calculation: it spreads principal and interest across equal monthly payments for the whole term (French amortization, the most common method for fixed-rate loans) -- it's not simple compound interest on a balance.
Health: BMI, calories and energy expenditure
BMI is calculated as weight (kg) divided by height (m) squared, using the WHO's standard categories (underweight, normal, overweight, obese) -- these are general categories, not adjusted for age, sex, build or muscle mass. The calorie and TDEE (total daily energy expenditure) calculators use the Mifflin-St Jeor equation for basal metabolic rate and multiply it by a factor based on your activity level; the result is an estimate meant as a starting point, not a medical or nutritional prescription.
Statistics and math
The average adds up every value and divides by how many there are; the median sorts the values and takes the middle one (or the average of the two middle ones if there's an even count) -- the median isn't pulled by an extreme value the way the average is. The rule of three solves a direct or inverse proportion: if A is to B, C is to what. For scientific work there are roots of any index, common and natural logarithms, all six trigonometric ratios and a degrees-to-radians converter. There are also GCD (greatest common divisor) and LCM (least common multiple) calculators for whole numbers, listed alongside the rest of this category's tools.
Physical quantities and units of measurement
The metric unit converters (length, mass, area and volume) cover the whole ladder of multiples and submultiples: each step is worth 10 for length and mass, 100 for area and 1000 for volume. To move to imperial and US units there are dedicated converters to inches, feet, miles, ounces, pounds, acres, gallons or pints, telling US and UK measures apart where they differ. There are also converters for temperature, time, energy, force, pressure, magnetism and data storage (including the difference between GB and GiB), all using exact defined factors or the conventional values stated on each tool. The LED equivalence calculator translates an LED bulb's actual watts into those of the incandescent bulb it replaces.
Orientative results, not advice
None of the calculators in this category replace financial, tax or medical advice. The result depends exactly on the data and assumptions you enter: the mortgage and loan calculators don't include insurance, origination fees or closing costs; the VAT calculator doesn't apply any country's legal rate automatically, it uses whatever percentage you type in; and the health calculators give a general estimate, not a diagnosis -- for real medical, tax or contractual decisions, consult a professional with your full details.
All of these calculators process the numbers directly in your browser: nothing is sent to a server.
Frequently asked questions
What's the difference between the percentage of an amount and percentage change?
The percentage of an amount calculates a value from a number and a percentage (20% of 50). Percentage change compares two values to see how much one changed relative to the other, and it can be negative if the value went down.
Are margin and markup the same thing?
No. Margin is calculated on the sale price, markup on the cost. For the same cost and price, markup always gives a higher percentage than margin.
What's the difference between simple and compound interest?
Simple interest is always calculated on the original principal. Compound interest is calculated on the principal plus interest already accumulated in earlier periods, so growth accelerates over time.
Does the mortgage or loan calculator include insurance, fees or closing costs?
No. It calculates the payment from the amount, interest rate and term, with fixed-payment amortization. Insurance, bank fees, closing costs or related taxes aren't included.
Is the BMI or calorie result a medical diagnosis?
No. They're general estimates based on standard formulas (WHO's BMI, the Mifflin-St Jeor equation), not adjusted for individual health conditions. For decisions about your health, consult a professional.
Why should I treat these results as orientative?
Because they depend exactly on the data and assumptions you enter, and none of these calculators account for taxes, fees or personal circumstances you haven't explicitly told it about.