How percentage decrease is calculated
A percentage decrease measures how much a value has fallen relative to its original amount. Like all percentage change calculations, it is expressed relative to the starting value — which means a 50% decrease always halves the original, regardless of the actual number.
% decrease = ((Original − New value) ÷ Original) × 100 Example: 200 → 150 → ((200 − 150) ÷ 200) × 100 = 25% New value = Original × (1 − Percentage ÷ 100) Example: 200 decreased by 25% → 200 × 0.75 = 150 Common percentage decrease reference
| % Decrease | Multiplier | 200 becomes | 500 becomes |
|---|---|---|---|
| 5% | × 0.95 | 190 | 475 |
| 10% | × 0.90 | 180 | 450 |
| 15% | × 0.85 | 170 | 425 |
| 20% | × 0.80 | 160 | 400 |
| 25% | × 0.75 | 150 | 375 |
| 50% | × 0.50 | 100 | 250 |
| 75% | × 0.25 | 50 | 125 |
| 100% | × 0.00 | 0 | 0 |
Formulas — both calculation modes
Find % change
Given an original value and a new value, the percentage change is the difference divided by the absolute original, multiplied by 100. A negative result is a decrease; positive is an increase.
% change = ((New − Original) ÷ |Original|) × 100 Original 1,000, New 750 → ((750 − 1000) ÷ 1000) × 100 = −25% Original 800, New 1,000 → ((1000 − 800) ÷ 800) × 100 = +25% Find new value
Given an original value and a percentage decrease, multiply the original by 1 − (rate ÷ 100).
New value = Original × (1 − Percentage ÷ 100) Original 1,000 decreased by 25% → 1,000 × 0.75 = 750 Original 500 decreased by 7.5% → 500 × 0.925 = 462.50 Scientific notation is supported
Both input fields accept standard scientific notation. This is useful when working with very large or very small numbers — you can type 1e6 instead of 1000000, or 5e-3 instead of 0.005. The calculator reads these exactly as JavaScript's Number() does.
| You type | Interpreted as | Example — 25% decrease |
|---|---|---|
| 1e3 | 1,000 | 1,000 → 750 |
| 2.5e2 | 250 | 250 → 187.50 |
| 1e6 | 1,000,000 | 1,000,000 → 750,000 |
| 5e-1 | 0.5 | 0.5 → 0.375 |
| 1.5e4 | 15,000 | 15,000 → 11,250 |
In the Find % change tab: entering 1e3 as both Original and New gives ((1,000 − 1,000) ÷ 1,000) × 100 = +0% — correct, because the value did not change. Entering 1e3 as Original and 7.5e2 as New gives −25%.
In the Find new value tab: entering 1e3 as Original and 25 as Percentage gives 1,000 × 0.75 = 750.
Frequently asked questions
What is the maximum possible percentage decrease?
100% — a 100% decrease reduces any value to zero. It is mathematically impossible to decrease something by more than 100% from a positive starting value, since you cannot go below zero using this formula. (A result below zero would require a starting value that itself was zero or negative, which the calculator treats as a special case.)
Is a 50% decrease the same as halving?
Yes, exactly. A 50% decrease multiplies the original by 0.50. A 50% decrease from 200 is 100. A 50% decrease from 80 is 40. The multiplier (0.50) stays constant regardless of the original value.
If a price drops by 20% and then by another 20%, is the total decrease 40%?
No. The second 20% is applied to the already-reduced price. Starting from 100: after the first 20% decrease you have 80. After a second 20% decrease you have 64 — a total decrease of 36%, not 40%. Successive percentage decreases compound, they do not simply add.
What does a positive result mean on the decrease calculator?
A positive percentage means the value actually increased from original to new. The calculator shows the true direction of change regardless of which mode you opened it in. You can also switch to Increase mode using the toggle at the top.
Does this calculator support scientific notation?
Yes. You can enter values like 1e3 (= 1,000), 2.5e2 (= 250), 1.5e4 (= 15,000), or 5e-1 (= 0.5). Standard JavaScript scientific notation is accepted in both the Original and New value fields. This makes it practical for very large or very small values without counting zeros. The result is always displayed in standard decimal form.
Does this calculator store my inputs?
No. All calculations run in your browser. Nothing is sent to a server or saved anywhere.