Build a monthly budget with four numbers
A useful budget starts with comparable amounts, simple categories and a clear distinction between expenses and goals.
Guides & advice
Practical explanations and examples to understand everyday numbers.
Money & finance Understand the calculation
Everyday life Understand the calculation
Watts and kilowatt-hours: power or consumption?
A device's power and the energy it consumes are different quantities. Usage time links them.
Mathematics Understand the calculation
Mean or median: what does each number tell you?
Two indicators can describe the same series and tell different stories. The choice depends on the question asked.
Everyday life Understand the calculation
Calculate journey cost without forgetting units
Distance, consumption and price per litre: three inputs estimate fuel. Other expenses are added afterwards.
Education & science Understand the calculation
Calculate your average with coefficients
A coefficient gives weight to a mark. A weighted average accounts for these differences without duplicating values.
Unit converters Understand the calculation
Convert length, area and volume
A factor of 100 is enough to go from metres to centimetres. For square or cubic metres, you need to go further.
Home & renovation Understand the calculation
How much paint should you allow for a room?
Area, number of coats and product coverage are enough to establish an initial consistent estimate.
Money & finance Understand the calculation
Markup and margin: choose the right denominator
The same gross margin in euros can give two different percentages. The rate depends on the value you compare it with.
Money & finance Understand the calculation
Loans: read the monthly payment and total cost
A small monthly payment tells only part of the story. Duration, interest and fees complete the comparison.
Money & finance Understand the calculation
Simple or compound interest: see the difference
The difference lies in what earns interest: the initial principal alone, or principal increased by previous interest.
Money & finance Understand the calculation
Do discounts of 20% and 10% add up to 30%?
Successive discounts apply to different prices. A simple example helps you check a promotion correctly.
Mathematics Understand the calculation
Percentages: the three calculations to know
A discount, a share of a budget, a price increase: the symbol is the same, but the calculation changes. Here is how to choose the right one.