Percentage gain calculator: measure growth from an old value to a new value
Percentage gain measures how much a value increased relative to its starting point. It is commonly used for prices, investment values, website metrics, sales, conversion rates and other before-and-after comparisons.
The standard calculation is (new value − old value) ÷ old value × 100. For example, moving from 80 to 100 is a gain of 20 on a starting value of 80, which equals a 25% increase.
Gain formula(new − old) ÷ old × 100
Positive resultPercentage increase
Negative resultPercentage decrease
Starting valueUsed as the denominator
Percentage increase and percentage decrease calculator
Percentage increase and decrease use the same percentage-change formula. If the new value is above the original value, the result is positive. If the new value is below it, the result is negative and represents a percentage decrease.
Always compare the change with the original value, not the new value. That denominator is what makes percentage change directional: increasing from 50 to 100 is a 100% increase, while decreasing from 100 to 50 is a 50% decrease.
What percent is one number of another?
To find what percentage one number is of another, divide the part by the total and multiply by 100. If 42 out of 60 items meet a condition, 42 ÷ 60 × 100 gives 70%.
This mode is useful for conversion rates, test scores, completion rates, budget shares, survey results and any situation where a part needs to be expressed as a percentage of a whole.
How to calculate a percentage of a number
To calculate X percent of a number, convert the percentage to a decimal and multiply it by the value. For example, 15% of 240 is 0.15 × 240 = 36.
This is useful for discounts, taxes, commissions, tips, markups and quick proportional calculations. If you are specifically calculating a sale price after a discount, the Discount Calculator can also show the final amount and savings directly.
Percentage of a total calculator: find a part as a share of the whole
Use the percentage-of-a-total calculation when you know a part and the overall total and want the part expressed as a percentage. Divide the part by the total and multiply by 100. For example, 18 completed tasks out of 24 total tasks equals 75%.
This is the same core relationship used for completion rates, budget shares, survey responses, test scores and conversion rates. Keep the total as the denominator; reversing the two values answers a different percentage question.
Formulapart ÷ total × 100
Example18 ÷ 24 × 100 = 75%
Common usesShares, rates, scores and completion
Percentage change vs percentage difference
Percentage change compares a new value with an original starting value, so direction matters. Percentage difference is used when neither value is naturally the starting point and measures the gap relative to the average of the two values.
Use percentage change for growth or decline over time. Use percentage difference when comparing two measurements, estimates or results where both values have equal status.