Percentage Decrease Calculator
How far a number has fallen in percentage terms — a price cut, a drop in sales, a reduction in weight or cost.
A decrease is measured against the starting value: (new − old) ÷ old × 100, which comes out negative when the number has fallen.
How the percentage decrease calculator works
A decrease is measured against the starting value: (new − old) ÷ old × 100, which comes out negative when the number has fallen. Note that a decrease can never exceed 100%, because the most a positive quantity can fall is to zero — a claim of "reduced by 150%" is a mistake, not a bargain.
Formula: X% of Y = Y × X / 100; X as % of Y = X / Y × 100; change = (B − A) / A × 100
Worked examples
| Inputs | Answer | Note |
|---|---|---|
| 80 down to 60 | -25% | −25% |
| A price cut from 120 to 90 | -25% | −25% |
| 1,000 down to 250 | -75% | −75% |
FAQFrequently asked questions
How do I calculate a percentage decrease?
Subtract the new value from the old, divide by the old, multiply by 100.
Can something decrease by more than 100%?
Not if it stays positive — falling to zero is exactly 100%. Anything more would mean going negative.
What is 25% off 80?
A reduction of 20, leaving 60.
How do I find the original price after a discount?
Divide, do not multiply back: 60 after 25% off is 60 ÷ 0.75 = 80.
Is a decrease the same as a discount?
Arithmetically yes, though discounts are usually quoted as the percentage taken off rather than a negative change.
Where these figures come from
- NIST Digital Library of Mathematical Functions — reference definitions for elementary and special functions
- Wolfram MathWorld — definitions and formulas for every topic on this page
- NIST/SEMATECH e-Handbook of Statistical Methods — the statistical formulas (mean, variance, z, confidence intervals, sample size)
- Australian Curriculum (ACARA) — Mathematics — the terms and methods taught in Australian schools
Last checked: September 2026. Formulas are fixed by mathematics and do not change with tax years or regulations.