๐ Percent Decrease Calculator: Find the Percentage Drop Between Two Values
By Shihab Mia ยท Updated 2026-08-03
Find the percent decrease
Enter the old (starting) value and the new (ending) value.
Percent decrease = (old - new) / old x 100.
Reverse: apply a percent decrease
Enter an old value and a percent decrease to get the new value.
Percent decrease tells you how much a value has dropped, expressed as a percentage of the original amount. Enter an old value and a new (smaller) value above and this tool instantly returns the percent decrease and the exact drop amount. If your new value is actually larger, it will flag that for you and point you to the right calculator instead.
What is the Percent Decrease Calculator?
Percent decrease measures how much something has shrunk relative to where it started. It answers a very specific question: out of the original 100%, what share disappeared? The formula is straightforward, percent decrease equals the old value minus the new value, divided by the old value, then multiplied by 100. That last step turns a plain fraction into a percentage that is easy to read and compare. A percent decrease is always reported as a positive number, since it describes the size of a drop, not a direction.
The most common mistake with percent decrease is dividing by the wrong number. The denominator must always be the original (old) value, not the new one and not the difference between them. This matters because the same dollar or unit drop produces a different result depending on where you started. Losing 20 from 80 is a 25% decrease, but losing 20 from 200 is only a 10% decrease, even though the raw drop is identical in both cases. Anchoring the calculation to the starting value is what makes this measure fair and comparable across very different scales.
Percent decrease is closely related to percent change and percent increase, but it is not interchangeable with them. Percent change can be positive or negative and covers both directions in one formula. It is the specific case where the value went down, and by convention it is stated without a negative sign, since "decrease" already tells you the direction. If you plug numbers in and the new value turns out to be bigger than the old value, you are not looking at a percent decrease at all, you are looking at a percent increase, and a different formula and a different calculator apply.
Understanding this concept well means being comfortable running the calculation in both directions. Sometimes you know the old and new values and want the percentage, which is the forward calculation this tool leads with. Other times you already know the target decrease you want to apply, such as a 25% markdown, and you need to find the resulting new value from an old value. That reverse calculation, new value equals old value times one minus the percent decrease as a decimal, is just as common in real budgeting, retail, and reporting work, which is why this page includes both directions side by side.
When to use it
- Working out how much a retail price dropped in percentage terms after a markdown or clearance sale.
- Tracking a percent decrease in weight, body fat, or another health metric between two checkpoints.
- Reporting a percent decrease in revenue, expenses, traffic, or any business metric between two periods.
- Checking a percent decrease in test scores, error rates, or other measurements over time.
- Applying a known percent decrease (like a 10% pay cut or a 20% discount) to find the resulting new value.
- Verifying a percentage drop that someone else has quoted, to confirm it was calculated correctly.
How to use the Percent Decrease Calculator
- Enter the old (starting) value in the first field of the main calculator.
- Enter the new (ending) value, which should be smaller than the old value for a true decrease.
- Read the percent decrease and the exact decrease amount from the results, updated instantly as you type.
- To go the other direction, use the reverse calculator below: enter an old value and a percent decrease to see the resulting new value.
Formula & method
Worked examples
A value drops from 80 to 60. What is the percent decrease?
- decrease amount = old - new = 80 - 60 = 20
- percent decrease = decrease amount / old x 100
- percent decrease = 20 / 80 x 100
- percent decrease = 0.25 x 100 = 25%
Result: Decrease amount is 20, percent decrease is 25%
A monthly electric bill falls from 150 to 114. What is the percent decrease?
- decrease amount = old - new = 150 - 114 = 36
- percent decrease = 36 / 150 x 100
- percent decrease = 0.24 x 100 = 24%
Result: Decrease amount is 36, percent decrease is 24%
Common percent decrease amounts from a starting value of 100
| Percent decrease | Old value | New value |
|---|---|---|
| 10% | 100 | 90 |
| 20% | 100 | 80 |
| 25% | 100 | 75 |
| 33% | 100 | 67 |
| 50% | 100 | 50 |
| 75% | 100 | 25 |
Percent decrease vs related percentage measures
| Measure | Compares | Sign kept? |
|---|---|---|
| Percent decrease | Old value to a smaller new value | No, always positive |
| Percent increase | Old value to a larger new value | No, always positive |
| Percent change | Old value to any new value | Yes, positive or negative |
Common mistakes to avoid
- Dividing by the new value instead of the old value. Percent decrease always divides by the original (old) value. Dividing by the new, smaller value inflates the result and does not match the standard percent decrease formula.
- Treating a percent increase as a percent decrease. If the new value is larger than the old value, the value went up, not down. That situation is a percent increase and needs the percent increase formula, not this one.
- Forgetting to multiply by 100. The ratio (old - new) / old is a decimal fraction, such as 0.25. Multiply by 100 exactly once to express it correctly as a percent decrease, like 25%.
- Mixing up the decrease amount with the percent decrease. The decrease amount is the raw drop in units (like 20 dollars). The percent decrease is that drop expressed relative to the old value (like 25%). They answer different questions and are not the same number.
Glossary
- Old value
- The starting or original value before the change occurred, used as the base of the percent decrease calculation.
- New value
- The ending value after the change, which is smaller than the old value in a true percent decrease.
- Decrease amount
- The raw difference between the old and new values, in the original units, before it is converted to a percentage.
- Percent decrease
- The decrease amount expressed as a percentage of the old value, always reported as a positive number.
- Percent increase
- The opposite case, where the new value is larger than the old value, calculated with a similar but distinct formula.
- Percent change
- A general term covering both percent increase and percent decrease, which keeps the sign to show direction.
Frequently asked questions
What is the formula for percent decrease?
Percent decrease equals the old value minus the new value, divided by the old value, then multiplied by 100. For example, from 80 to 60, that is (80 - 60) / 80 x 100 = 25%.
How do I calculate percent decrease?
Subtract the new value from the old value to get the decrease amount, divide that by the old value, then multiply by 100. This calculator does all three steps for you and shows both the decrease amount and the resulting percentage.
Is percent decrease always positive?
Yes. It describes a drop, so it is reported as a positive number by convention. If your calculation gives a negative result, the value actually increased, which calls for the percent increase formula instead.
What is the percent decrease from 80 to 60?
The percent decrease from 80 to 60 is 25%. The decrease amount is 20 (80 minus 60), and 20 divided by 80, times 100, equals 25%.
How do I find the new value after a percent decrease?
Multiply the old value by (1 minus the percent decrease as a decimal). For a 25% decrease from 80, that is 80 x (1 - 0.25) = 80 x 0.75 = 60. Use the reverse calculator above for this direction.
What is the difference between percent decrease and percent change?
It is a specific, always-positive measure used only when the value went down. Percent change is a broader term that covers both increases and decreases and keeps a positive or negative sign to show which direction the value moved.