Percentage Decrease Calculator
Calculate the percentage decrease from an original value to a lower one. Get the percent decrease as a positive figure, the amount it dropped, and how much remains — perfect for discounts, markdowns, and price drops.
ToolsSoup's Percentage Decrease Calculator tells you exactly how much a number has dropped, as a percentage. Enter the original value and the new, lower value, and you instantly get the percentage decrease as a clean positive figure, the exact amount the value fell by, and how much is left as a percent of the original. It's the quickest way to answer questions like "what is the percentage decrease from 100 to 80?" and to work out discounts, price drops, markdowns, sale reductions, weight loss, falling traffic, or any drop from a before value to a smaller after value. Everything runs in your browser — no uploads, no sign-up, and your numbers never leave your device.
What is a percentage decrease calculator?
A percentage decrease calculator measures how far a number has fallen from its starting point, expressed as a percentage of the original. Unlike a generic percent-change tool, it is built around reductions: you put in the original (higher) value and the new (lower) value, and it reports the decrease as a positive percentage — for example a drop from 100 to 80 is a 20% decrease, not −20%. If you accidentally enter a new value that is larger, it flags that the change is actually an increase, so you always know you are reading a genuine decrease.
How to calculate percentage decrease
Working out a percentage decrease takes three quick steps, and this tool does them automatically as you type:
- Enter the original value in the first field — the starting amount before it dropped.
- Enter the new, lower value in the second field — the amount after the reduction.
- Read the percentage decrease. The result is shown as a positive percent, with the amount of the drop and the remaining percentage of the original underneath.
What is the percentage decrease formula?
The percentage decrease formula is: ((original value − new value) ÷ original value) × 100. Subtract the new value from the original to get the amount of the drop, divide that by the original value, and multiply by 100 to turn it into a percentage. For example, a fall from 100 to 80 is ((100 − 80) ÷ 100) × 100 = 20%, so it is a 20% decrease. Because the decrease is measured against the original value, the result is always reported as a positive percentage representing how much was taken away.
Calculating a discount or markdown
Percentage decrease is the same calculation as a discount or markdown. If a $100 jacket is on sale for $80, enter 100 as the original value and 80 as the new value: the calculator shows a 20% decrease, a drop of $20, and 80% remaining — in other words you pay 80% of the original price and save 20%. This makes it handy for checking sale prices, clearance markdowns, and "X% off" deals.
Percentage decrease vs percentage increase
A decrease and an increase use the same arithmetic, but a decrease is reported as a positive percentage of how much the value fell, while an increase describes growth. A key catch is that they do not cancel out, because each is measured against its own starting value: cutting 100 by 20% gives 80, but raising 80 back by 20% only gives 96, not 100. If you need to measure growth instead, use the percentage increase calculator; this tool is tuned for reductions and even warns you when the new value is actually higher.
Why use this percentage decrease calculator?
- Purpose-built for reductions: enter an original value and a lower value and get the drop instantly.
- Shows the percentage decrease as a clean positive number, the way you'd say it out loud ('a 20% decrease').
- Also gives the exact amount of the drop and how much remains as a percent of the original — ideal for discounts and markdowns.
- Warns you if the new value is actually higher, so you never mistake an increase for a decrease.
- Updates live as you type, runs entirely in your browser, and is 100% free with no ads or sign-up.
Frequently asked questions
How do I calculate the percentage decrease between two numbers?
Subtract the new value from the original, divide by the original, and multiply by 100. For example, from 100 to 80 is ((100 − 80) ÷ 100) × 100 = 20%. Enter both numbers above and the calculator does it for you instantly.
What is the percentage decrease from 100 to 80?
It is a 20% decrease. The amount of the drop is 20, and 20 divided by the original value of 100 is 0.2, which is 20%. The new value of 80 is 80% of the original.
How do I work out a discount percentage?
A discount is just a percentage decrease from the original price to the sale price. Enter the original price as the original value and the sale price as the new value — the calculator shows the discount percent, the amount you save, and the percentage of the original price you still pay.
What happens if I enter a new value that is higher than the original?
The result becomes negative, which means the value actually went up, so the calculator flags it as an increase rather than a decrease. For a genuine percentage decrease the new value must be lower than the original.
What happens if the original value is zero?
Percentage decrease from zero is undefined, because you cannot divide by zero, so the percent shows a dash. The calculator still shows the raw amount of the change in that case.