How to Calculate Percentage Decrease
Learn how to calculate percentage decrease between an original and a new value.
Key idea
Learn how to calculate percentage decrease between an original and a new value.
Formula or method
Worked example
Start with the values in your question, substitute them into the formula, and keep the units consistent. For example, if a rate is given as 15%, use 0.15 when a formula requires a decimal.
Common mistakes
- Mixing percentage points with percentage change.
- Using different units for the same calculation.
- Rounding too early when several steps are involved.
Why the result can differ
Real-world calculations can include assumptions, rounding, fees, tax rules, calendar conventions, or other details. Treat simple calculator results as estimates when the underlying situation is more complex.
Choosing the reference value
Percentage decrease is measured relative to the original value. If a quantity falls from 250 to 200, the decrease is 50 and the percentage decrease is 50 ÷ 250 × 100 = 20%.
Why the reverse calculation differs
A 20% decrease followed by a 20% increase does not return to the original value. Starting at 250, a 20% decrease gives 200, and a 20% increase on 200 gives 240. The second percentage uses a different base.
Quick check
Keep the original value visible while working. It should be the denominator in the percentage-decrease formula.