Percentage Calculator
Three modes: percent of, what-percent, change between two values.
Written by Anil Gautam · Updated
Which percentage mode should you pick?
Each tab answers a different question. X% of Y multiplies the two numbers and divides by 100, so 18% of 2,450 is 441, the GST on a ₹2,450 bill at 18%. X as % of Y divides the first number by the second and multiplies by 100: 45 out of 60 is 75.00%. Change from X to Y expresses the difference between the two numbers as a share of the first, so a price going from ₹1,200 to ₹1,500 is up 25.00%, and the reverse move shows -20.00%.
Successive changes compound. Two 10% rises in a row come to 21.00% in total: 10% of 100 is 10, 10% of 110 is 11, and the change tab shows 21.00% from 100 to 121.
Why does a 20% fall need a 25% rise to recover?
Percentage change is always measured against the starting value, so the same gap gives a different answer in each direction. A fall from 100 to 80 is -20.00%. Climbing back from 80 to 100 is 25.00%, since the base is now 80.
GST causes the same confusion. On a ₹1,000 item, 18% GST adds ₹180 and the bill becomes ₹1,180. Ask what percentage 180 is of 1,180 and the tool says 15.25%, because the tax is now compared with the bill. To take GST out of a price that already includes it, the GST Calculator does the division for you.
Interest rates add one more trap. A rate moving from 8% to 10% rises by 2 percentage points, while the change tab reports 25.00%, the relative change. Use percentage points when you mean the gap between two rates.
What happens with zero, negative numbers and pasted values?
The boxes keep only digits, a decimal point and a minus sign, so you can paste 1,500 or ₹2,450.50 and the commas and symbol drop out. Dividing by zero has no answer: when Y is 0 in the X as % of Y tab, or X is 0 in the change tab, the tool shows 0.00%, which you should read as undefined. A negative starting value flips the sign, so a loss of 50 turning into a profit of 50 shows as -200.00% even though the figure went up.
Copy puts the unrounded number on the clipboard without a percent sign, so 1 as a percentage of 3 copies as 33.33333333333333 while the screen shows 33.33%. Results in the first tab use international comma grouping and up to four decimal places, for example 154,320.875 for 12.5% of 1,234,567.