1. What is X% of Y?
2. X is what percentage of Y?
3. Percentage change
Useful for discounts, margins, changes in revenue, price movements and other everyday financial comparisons.
Common percentage calculations
Percentages are widely used in finance for discounts, returns, profit margins, interest rates, changes in sales and comparing one amount with another.
X% of Y = (X ÷ 100) × Y
Percentage Share = (Part ÷ Whole) × 100
Percentage Change = ((New − Original) ÷ Original) × 100
Worked examples
20% of 250 is 50. If 50 is compared with a total of 250, it represents 20%. If a value rises from 200 to 250, the percentage increase is 25%.
How to interpret percentage change
A positive result means an increase and a negative result means a decrease. Percentage change depends on the original value, so reversing the starting and ending values does not produce the same percentage.
When this calculator is useful
Percentages appear throughout everyday finance. This tool is useful for discounts, price changes, revenue growth, investment gains or losses, budget shares and simple comparisons between two values.
Worked examples
Example 1: Discount
20% of £250 is £50. A 20% discount on a £250 item therefore reduces the price to £200.
Example 2: Revenue growth
If revenue rises from £40,000 to £50,000, the increase is £10,000, which is a 25% increase relative to the original value.
Common mistakes to avoid
- Using the new value as the denominator when calculating a percentage increase from the old value.
- Assuming percentage increase and percentage decrease are symmetrical.
- Confusing percentage points with percentage change.
- Using percentage change when the original value is zero.
Assumptions and limitations
The calculator performs arithmetic only. It does not determine whether a percentage is financially meaningful or appropriate for a particular decision. Percentage change from an original value of zero is undefined.
Related calculators
Profit Margin Calculator · Investment Return Calculator · VAT Calculator
Frequently asked questions
How do I calculate a discount?
Calculate the discount percentage of the original price, then subtract that amount from the original price.
Why is percentage decrease different when reversed?
Because the denominator changes. A rise from 100 to 125 is 25%, but a fall from 125 to 100 is 20%.
Can this be used for profit margins?
It can calculate generic percentages, but for business profitability use the dedicated Profit Margin Calculator because margin and markup use different formulas.