How does the Percentage Calculator work?
Percentage value = base × percent ÷ 100. The calculator also shows the base plus and minus that value.
Background & details
The percentage calculator gives you three numbers: the percentage value (X % of Y), the base value plus that amount (a mark-up) and the base value minus that amount (a discount). One input therefore covers discounts, mark-ups, tip estimates and tax in a single view.
How to read the result
The percentage value on its own tells you nothing about whether something is expensive or cheap – it is only a share. It only means something in context: 15 % of €200 is €30, but 15 % of €2,000 is €300. Always be clear about which base value (the “100 % reference”) you are working from.
Common mistakes
- Confusing mark-up and discount: raising a price by 20 % and then cutting it by 20 % does not return you to the original – you land at 96 % of it, because the second percentage applies to the already-increased number.
- Mixing percent and percentage points: if an interest rate moves from 2 % to 3 %, that is 1 percentage point more, but a 50 % relative increase. Headlines often get this wrong.
- Wrong base: in “X is Y % higher than Z”, Z (the starting value) must be the base, not X.
Practical tips
For mental maths, use the 10 % rule: get 10 % by moving the decimal point one place left (10 % of 80 = 8). From there almost everything follows – 5 % is half, 20 % is double, 1 % is a tenth of it. For a quick 15 % estimate, add 10 % plus half of that.
A handy trick: X % of Y always equals Y % of X. 8 % of 50 is the same as 50 % of 8 (both are 4) – sometimes the flipped version is far easier in your head.
When a different calculator fits better
If you need a percentage change over several years with compounding (saving or inflation, for example), a single percentage value is not enough – use a compound-interest or inflation calculator for that. For plain discounts or VAT, the dedicated tools are quicker because they return the result straight as a price.