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Compound interest lets your gains generate interest of their own. Over 10 years, starting with €1,000 and adding €100/month at 5%, you end up with about €17,175.

Finance

A mortgage's monthly payment is calculated from the amount borrowed, the annual interest rate, and the term. Example: a €200,000 loan at 3.5% over 20 years gives a monthly payment of about €1,159.92, for a total loan cost of €278,380.66 (that is, €78,380.66 in interest).

Finance

To calculate X% of a number, multiply that number by X and then divide by 100. For example, 20% of 50 is calculated as: 50 × 20 ÷ 100 = 10.

Mathématiques

To go from a net (tax-excluded) amount to a gross (tax-included) amount, multiply the net amount by the VAT rate, then add that result to the net amount. Example: €100 net at a 20% VAT rate gives €20 of VAT, for a €120 gross total.

Mathématiques

To calculate a price after a discount, multiply the original price by the discount percentage to get the discount amount, then subtract that amount from the original price. Example: €100 with a 20% discount gives €80 (discount amount: €20).

Mathématiques

A circle's area is π × radius², and its perimeter (circumference) is 2 × π × radius. For a circle with a 5 cm radius, the area is about 78.54 cm² and the perimeter is about 31.42 cm.

Mathématiques

The Pythagorean theorem gives the hypotenuse of a right triangle with the formula √(a² + b²), where a and b are the two legs forming the right angle. For a 3-4 triangle, the hypotenuse is exactly 5.

Mathématiques

Ohm's law gives the voltage of an electrical circuit with the formula U = R × I, where R is resistance in ohms and I is current in amps. For a resistance of 10 Ω carrying a current of 2 A, the voltage is 20 V.

Physique

To calculate a tip, multiply the bill amount by the desired percentage. Example: on a €50 bill, a 15% tip is €7.50, for a total of €57.50.

Quotidien

Your age in full years is calculated by counting the complete years elapsed from your date of birth to today — the current year only counts if your birthday has already passed.

Quotidien

To convert Celsius to Fahrenheit, multiply by 9/5 and add 32 (0 °C = 32 °F). To convert to Kelvin, add 273.15 to the Celsius value (0 °C = 273.15 K).

Conversion

BMI is calculated by dividing weight (in kg) by the square of height (in meters). Example: for 70 kg and 1.70 m, BMI is 70 ÷ 1.70² ≈ 24.2, which falls in the normal weight category according to the WHO.

Santé

Your daily calorie needs depend on your basal metabolic rate (the energy spent at rest) multiplied by your physical activity level. This calculator shows a range rather than a single figure, since it is an estimate: actual energy expenditure varies between people beyond what these formulas can capture.

Santé

The area of a rectangular room is found by multiplying its length by its width. Example: a room measuring 4 m by 3 m has an area of 12 m².

Bricolage

The amount of paint needed is found by multiplying the surface to paint by the number of coats, then dividing by the paint's coverage (shown on the can, in m²/L). Example: 20 m² with 2 coats and a coverage of 10 m²/L requires 4 L of paint.

Bricolage