The same maths phrased three ways — pick the one matching the question in your head.
Going from 10% to 15% is a rise of 5 percentage points but a 50% increase — the third box computes the latter. News headlines mix these up constantly; now you don’t have to.
“It costs 124 including 24% VAT — what was it before?” is not “minus 24%”. That one lives on its own page: the VAT calculator.
Yes — 12,5 and 12.5 both work, and thousands separators are fine
(1,234.56 or 1.234,56). A lone comma followed by exactly three digits,
like 1,234, is read as one thousand two hundred thirty-four.
Entirely in your browser. Numbers you type are never sent anywhere — there is no server doing the math, no analytics watching you do it.