The six calculators

Percent of a number answers “what is 15% of 80?” by multiplying and dividing by 100. Part of a whole turns it around: 20 out of 50 is 40%.

Percent change compares a start and an end value: from 80 to 100 is a 25% increase, from 100 to 80 a 20% decrease. The change is always measured against the starting value, which is why going up 25% and then down 25% does not get you back to where you began.

Increase or decrease adds or takes off a percent. Find the original undoes an added percent, for example the price before 20% tax was added. Sale price takes one discount, or two in a row; the second is taken off the already reduced price, so 20% then 10% off is 28% off in total, not 30%.

Questions

How do I work out a tip or split a bill? Use “Percent of a number” with the bill and the tip percent, then add the result to the bill.

Why does it say the number can’t be zero? A percent compares one number with another, and there is no percent of nothing. Change the starting value to see an answer.

Can I type commas? Yes. 1,250.50 works, and so does 12,5 as a decimal comma. Nothing you type leaves your device.