Percentage Calculator Guide: Formula & Worked Example
Short answer
What is X% of Y, X as a percent of Y, and more. In the fixed example below, x% of y is 30. Your answer depends on the inputs and assumptions you choose.
Formula
Result = Percentage Calculator calculation using value x, value y
The inputs are value x, value y. Use the input scale shown beside each field and keep time periods and units consistent. Only round the final result for display.
Worked example
- Value X
- 20
- Value Y
- 150
- X% of Y: 30
- X is what % of Y: 13.3333%
- Y is what % of X: 750%
- Y increased by X%: 180
- Y decreased by X%: 120
Understanding the result
What is X% of Y, X as a percent of Y, and more. Start with the base example, then replace each value with the figure that matches your situation.
Value X
The example uses 20 for value x. This is an illustration, not a recommended value. Keep the unit and time period shown by the field.
Value Y
The example uses 150 for value y. This is an illustration, not a recommended value. Keep the unit and time period shown by the field.
What the comparison means
The comparison changes only value x, keeping every other example input fixed. This isolates that input's effect on the primary result. It does not predict future outcomes.
Check units, date boundaries and rounding before using the answer in a report or a practical measurement.
Percentage formulas at a glance
| Question | Formula | Example | |---|---|---| | What is X% of Y? | (X ÷ 100) × Y | 20% of 150 = 30 | | X is what percent of Y? | (X ÷ Y) × 100 | 30 is 20% of 150 | | Percentage change from A to B | ((B − A) ÷ A) × 100 | 80 → 100 = +25% | | Increase Y by X% | Y × (1 + X ÷ 100) | 150 + 20% = 180 | | Decrease Y by X% | Y × (1 − X ÷ 100) | 150 − 20% = 120 | | Find the original before a % increase | New ÷ (1 + X ÷ 100) | 180 after +20% → 150 |
People also ask
How do I calculate a percentage in my head?
Find 10% by moving the decimal one place left, then scale. 10% of 240 is 24, so 5% is 12 and 15% is 36. For 1%, move the decimal two places: 1% of 240 is 2.4.
Why doesn't a 50% drop followed by a 50% rise get me back to the start?
Each percentage is applied to a different base. 100 falls 50% to 50, and 50 rising 50% is only 75. To recover a 50% loss you need a 100% gain.
What is the difference between percent and percentage points?
If an interest rate goes from 4% to 5%, it rose by 1 percentage point but by 25 percent of its original value. News and finance often mix these up.
How do I reverse a discount or sales tax?
Divide, don't subtract. A price of 92 after a 20% discount was 92 ÷ 0.8 = 115, not 92 + 20% = 110.4.
Real-life uses
- Shopping: compare "30% off" with "buy 2 get 1 free" (that is 33.3% off per item).
- Salary: a raise from 50,000 to 54,000 is (4,000 ÷ 50,000) × 100 = 8%.
- Grades: 42 correct out of 60 is 70%.
- Investing: a portfolio moving from 12,000 to 13,500 returned 12.5%.
Comparison
| Scenario | Input | Result |
|---|---|---|
| Lower input | Value X: 16 | X% of Y: 24 |
| Base example | Value X: 20 | X% of Y: 30 |
| Higher input | Value X: 24 | X% of Y: 36 |
Common mistakes
- Using the wrong units for value x.
- Comparing results while changing more than one input at a time.
- Check units, date boundaries and rounding before using the answer in a report or a practical measurement.
Checklist
- Confirm value x.
- Confirm value y.
- Check the result against your source or provider.
Calculators Percentage Editorial Team
Calculator guides from the Calculators Percentage team. These introductory examples are educational, not professional advice.
Last reviewed:
Check units, date boundaries and rounding before using the answer in a report or a practical measurement.