How percentage calculations work
Percentages express a part of a whole using 100 as the reference. This calculator keeps the arithmetic visible so you can check a rate, compare two measurements, or estimate a sale price. For online purchases, also review the Federal Trade Commission online-shopping guidance and the seller terms before relying on an advertised discount.
How to use this calculator
Choose a mode, enter non-negative values, and calculate. For percentage change, use the earlier figure as the original value and the later figure as the new value. For discounts, the result is the price after the reduction, while the breakdown shows the amount saved.
Quick percentage reference
These examples show how common rates relate to a base of 100. The same relationship scales to any non-negative base value.
| 10% | 10 parts out of every 100; divide the base by 10. |
|---|---|
| 25% | 25 parts out of every 100; one quarter of the base. |
| 50% | 50 parts out of every 100; one half of the base. |
What these items mean
Base value: the whole or starting amount that the percentage is applied to. Percentage: a rate expressed per 100, a convention developed through mathematics and accounting rather than by one single creator. Percentage change: the relative difference between an original and a new value. Discount rate: the percentage removed from an original price.
Interpretation and limits
The result is arithmetic, not a guarantee about taxes, fees, shipping, inflation, currency conversion, rounding rules, or a seller’s advertised terms. Check the original numbers and units before using the result in a purchase, report, or financial decision.