Percentage Calculator
Three everyday percentage tasks: p percent of x, what percent x is of y, and change from x to y.
What is p% of x?
x is what percent of y?
Change from x to y
What is it
Three questions come up constantly in daily life and they are three different formulas: (A) p percent of x means x times p divided by 100. (B) x is what percent of y means x divided by y times 100. (C) the change from x to y means (y minus x) divided by x times 100 — a positive number is growth, a negative one is a drop. All three panels here update live as you type.
Notes & fun facts
Percentages are really just fractions out of 100, which is why the Romans already used them: their taxes on goods were often levied "per centum" — per hundred. The % sign itself is a slow deformation of a small "100" written next to a number, with the two zeros becoming circles and the 1 shrinking into a diagonal line.
Origin & history
Calculating "per hundred" shares goes back to Roman tax administration of the 1st century BC, where duties like the centesima rerum venalium (one hundredth of auction sales) were standard. The modern percent sign appears in print around 1650, and percentage arithmetic became a schoolroom staple in Europe from the 16th century onward, as trade and bookkeeping demanded quick proportion math.