Percentage Decrease Calculator
Find the percentage decrease between two values, apply a known percentage decrease to a number, or work backward to the original value from a reduced value and percentage.
Works with any numbers \u2014 prices, weights, scores, populations, anything that goes down. Find % Decrease tells you how big the drop was between two values, Apply a Decrease reduces a starting value by a percentage you already know, and Find Original Value works backward from a reduced number to what it was before the decrease. Results update instantly as you type.
How to Use This Calculator
- Have both the original and the new value? Use Find % Decrease to see exactly how big the drop was.
- Know a starting value and a percentage you want to take off? Use Apply a Decrease to see the resulting number.
- Only know the reduced value and the percentage it fell by? Use Find Original Value to work out what it started at — useful when you don't have the original number on hand.
- Results and the formula used update live as you type, though the Calculate button is there too.
Understanding Percentage Decrease
A percentage decrease measures how much a value dropped, relative to where it started. That "relative to" part matters — a $10 drop means something very different on a $20 item than it does on a $500 one, which is exactly why percentage is the more useful number to compare across different scales. Percentage decrease and percentage increase use the same underlying formula; the only real difference is which direction the number moved.
The Formulas, With Worked Examples
Percentage decrease between two values:Percentage Decrease = ((Original − New) ÷ Original) × 100
Example: a value drops from 200 to 150. (200 − 150) ÷ 200 × 100 = 25%.
Applying a known percentage decrease:New Value = Original − (Original × Percentage ÷ 100)
Example: 43 decreased by 26% is 43 − (43 × 0.26) = 43 − 11.18 = 31.82.
Finding the original value without knowing it directly:Original = New ÷ (1 − Percentage ÷ 100)
Example: if a value fell 20% to reach 72, the original was 72 ÷ 0.80 = 90.
Quick Reference: Common Percentage Drops
A fast lookup for the percentages people check most often, on two common starting values.
| Decrease | From 100 | From 500 |
|---|---|---|
| 10% | 100 → 90.00 | 500 → 450.00 |
| 20% | 100 → 80.00 | 500 → 400.00 |
| 25% | 100 → 75.00 | 500 → 375.00 |
| 30% | 100 → 70.00 | 500 → 350.00 |
| 50% | 100 → 50.00 | 500 → 250.00 |
Frequently Asked Questions
How do you calculate a percentage decrease?
Subtract the new value from the original value, divide that difference by the original value, then multiply by 100. Dropping from 200 to 150 is a decrease of 50, and 50 ÷ 200 × 100 = 25%.
How do I calculate percent increase or decrease?
Both use the same core formula — (New − Original) ÷ Original × 100 — the only difference is the sign. A positive result means an increase; a negative result (or the original being larger than the new value) means a decrease.
How do I calculate a 20% decrease?
Multiply the value by 0.20 to find the amount it drops by, then subtract that from the original. On 90, a 20% decrease is 90 × 0.20 = 18, so the result is 72. The Apply a Decrease tab above does this instantly for any starting number and percentage.
What is 43 decreased by 26%?
43 × 0.26 = 11.18, so 43 decreased by 26% is 43 − 11.18 = 31.82.
How do I calculate percentage decrease without knowing the original number?
If you know the reduced value and the percentage it was decreased by, you can work backward: Original = Reduced Value ÷ (1 − Percentage ÷ 100). Use the Find Original Value tab above and it’s calculated for you.
What’s the difference between percentage decrease and percentage change?
"Percentage change" is the general term that covers both directions. "Percentage decrease" specifically means the new value is lower than the original — the result is always expressed as a positive drop, even though the underlying change is negative.
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Last updated: September 14, 2026