Going from 20 to 15 is a 25% decrease.
Worked out below step by step, with a table of related values and a live calculator so you can change the numbers.
Check it: 20 − 5 = 15, the new value.
percent change = (new − old) ÷ old × 100
Percent change always compares the difference against the original value, not the new one.
Percentage change uses the starting value as the reference. The numerical change is -5; divide that change by the original 20, then multiply by 100.
The result is 25%. A positive answer is an increase and a negative answer is a decrease. Because the original value is the denominator, changing the direction of comparison gives a different percentage.
The ratio of the new value to the starting value is 0.75. Comparing that multiplier with 1 shows how far the new value sits below the starting value in percentage terms.
What is the percent change from 20 to 10?
Find the difference: 10 − 20 = -10. Divide by the original value: -10 ÷ 20. Multiply by 100: that is a 50% decrease. This uses the same method with different numbers, so it shows how the rule transfers instead of only repeating the original answer.
The numerical difference is 5, a decrease. Relative to the starting value 20, that difference represents 25%. The starting value matters because percentage change measures the difference against the original baseline, not the final value.
Percentage change is used for price movement, growth, energy use, production, traffic and performance comparisons. It is most meaningful when the starting value is clearly defined and the direction of change is reported with the percentage.
The ratio of the new value to the starting value is 0.75. Comparing that multiplier with 1 shows how far the new value sits below the starting value in percentage terms. New ÷ original = 15 ÷ 20 = 0.75. Subtract 1: 0.75 − 1 = -0.25. Multiply by 100 to get 25% decrease.
Using the final value 15 as the denominator instead of the starting value 20. After correcting that setup, verify the result independently: Check it: 20 − 5 = 15, the new value.
Yes. What is the percent change from 20 to 10? Find the difference: 10 − 20 = -10. Divide by the original value: -10 ÷ 20. Multiply by 100: that is a 50% decrease. This uses the same method with different numbers, so it shows how the rule transfers instead of only repeating the original answer. The live calculator above lets you replace both inputs and recalculate without changing the underlying method.
The numerical difference is 5, a decrease. Relative to the starting value 20, that difference represents 25%. The starting value matters because percentage change measures the difference against the original baseline, not the final value. Use that scale or ratio check together with the reverse calculation before reusing the result in another calculation.
| New value | Percent change |
|---|---|
| 10 | −50% |
| 15 | −25% |
| 18 | −10% |
| 22 | +10% |
| 25 | +25% |
| 30 | +50% |
| 40 | +100% |