Number & Math
Percentage Calculator
X% of Y, percentage change, reverse percent, and tip / tax modes.
Mode
Inputs
Result
30
20% of 150 = (20 / 100) × 150 = 30
About this tool
Five common percentage operations in one tool: (1) what is X% of Y, (2) X is what percent of Y, (3) percentage change from X to Y, (4) reverse - X is N% of what, (5) add / subtract a percent (tax, tip, discount). Each mode shows the worked formula so you can sanity-check the answer.
FAQs
How is percentage change calculated?
(new - old) / old * 100. A change from 200 to 220 is (220 - 200) / 200 * 100 = 10%. From 200 to 180 is (180 - 200) / 200 * 100 = -10%.
When is the reverse percent useful?
When you know the discounted price and the discount rate but want the original. '$80 is 20% off what?' → original was $100. Or 'gross-up VAT': if $118 includes 18% VAT, net = 118 / 1.18 = $100.
How is 'add 18% tax' different from 'gross-up 18%'?
Add 18%: new = old * 1.18 (net to gross). Gross-up: new = old / 1.18 (gross to net). The first converts pre-tax to post-tax, the second reverses it.
Are negative percentages allowed?
Yes - a negative percent change means a decrease. A negative percent of Y is a negative number. Useful for losses, discounts and reverse markups.
Does it handle compound percent changes?
Yes - a multi-step mode lets you apply a sequence of changes (e.g. +10% then -10%, which doesn't return to the original) and see the cumulative effect.