Five percentage calculations in one
People search for these one at a time, but they’re all the same idea: a percentage is just a fraction of 100. Pick the tab you need and the result updates as you type.
- % of a number: how much is 20% of 80?
- What % is: what percent of 180 is 45?
- % change: how much did something go up or down?
- Discount: what’s the final price after a percentage off?
- Sales tax: what’s the price with tax, or without it?
How to calculate a percentage of a number
result = number × percentage ÷ 100. So 20% of 80 is 16.
The everyday version is the tip. On a $64 check, 15% is $9.60 and 18% is $11.52. To do it in your head, find 10% by moving the decimal point ($6.40), then add half of it for 15% or double it for 20%.
What percent is one number of another
percentage = part ÷ total × 100. If you got 45 questions right out of 180, that’s 45 ÷ 180 × 100 = 25%.
Percent increase and decrease
change = (new − old) ÷ old × 100. Rent going from $1,200 to $1,450 is a 20.83% increase. Always divide by the starting value: that’s why a 50% drop followed by a 50% rise doesn’t get you back to where you started.
Watch out for percentage points. If an interest rate moves from 4% to 5%, it went up 1 percentage point, which is a 25% increase in the rate itself.
Discounts
final price = price × (1 − discount ÷ 100). A $89.90 jacket at 30% off costs $62.93.
Stacked discounts don’t add up: 20% off and then an extra 10% off is a 28% discount, not 30%, because the second one applies to the reduced price.
Sales tax
To add tax: total = price × (1 + rate ÷ 100). At 7.25%, $1,000 becomes $1,072.50. In New York City, where the combined rate is 8.875%, a $59.99 item costs $65.31 at the register.
To remove tax from a total: price = total ÷ (1 + rate ÷ 100). $1,072.50 at 7.25% is exactly $1,000. The common mistake is subtracting 7.25% of the total, which gives $994.74: the tax was calculated on the price, not on the total, so you have to divide.
There’s no national sales tax in the US: rates are set by states, counties and cities, which is why the calculator lets you type your own. Alaska, Delaware, Montana, New Hampshire and Oregon have no statewide sales tax, although some Alaskan towns charge a local one.
When a percentage isn’t enough
If you know three values and need the fourth, for example scaling a recipe or working out a unit price, a proportion is the right tool. Try the proportion calculator.