Percentage calculator

How to use this page

1. Replace the sample numbers with your own. Nothing is sent to a server.
2. Read the result. It changes as you type.
3. Open the formula if you want to recompute the result by hand.
4. Copy the result if you want to keep it. The numbers you type stay in this browser and are not added to the address.

Formula

Percent of: result = B × A ÷ 100. What percent: result = A ÷ B × 100. Change from A to B: (B − A) ÷ A × 100. Add a percent: A × (1 + B ÷ 100). Subtract a percent: A × (1 − B ÷ 100). A check: 15% of 80 is 12. From 80 to 100 is a 25% increase, because the base is 80, not 100.

The base is the sensitive part

A change uses the starting number as the base. Falling from 100 to 80 is a 20% drop. Rising from 80 back to 100 is a 25% rise. Both moves are 20 units. The percents differ because the bases differ. If you mix them up, a discount and a markup will not undo each other.

What-percent and percent-change both refuse a zero base. Percent of a zero amount is zero, which is allowed. Adding a percent to zero stays zero.

Where this sits next to the other tools

Use this page for a single percent. Use the discount page when two markdowns stack and tax arrives after the sale price. Use the sales-tax page when you need to pull tax back out of a total. Use the loan page for interest that compounds on a balance for many months. A percent change is not a compound rate.

The numbers are unitless. If you are thinking in won, yen, dollars, or people, the result is in that same unit. The currency switch does not rescale a percentage result.

Easy mistakes

• Dividing by the ending value when you meant the starting value.
• Stacking two discounts by adding the percents. 20% then 10% off is not 30% off. The discount page does the sequence.
• Treating a monthly rate multiplied by 12 as an effective annual rate. Multiplying by 12 gives the nominal annual rate; the effective annual rate includes compounding.