Percentage Decrease Calculator

Percentage decrease calculator for price drops, discounts, and performance declines

A percentage decrease tells you how much a value went down compared to where it started. This is the common “percent drop” you see in discounts, price reductions, cost savings, sales declines, test score drops, weight changes, and any before-and-after comparison where the second number is lower than the first.

This calculator gives you two outputs at once: the decrease amount (the raw difference between the original and new values) and the percentage decrease (the difference as a percentage of the original). Seeing both is useful because they answer different questions. The amount tells you “how many units” you lost or saved. The percent tells you “how big the change is” relative to the starting point.

To use it, enter your original value (the “before” number) and your new value (the “after” number). For example, if something costs 250 and it now costs 200, the decrease amount is 50 and the percentage decrease is 20%. The calculator also handles cases where the new value is higher than the original. In that situation, the result is not a decrease, it is an increase, and the percentage will be shown as negative to reflect that the value did not drop.

Assumptions and how to use this calculator

• The original value must be greater than 0, because percentage decrease is based on the original as the denominator.
• The new value can be 0 or higher. If your new value is 0, the decrease is 100%.
• If the new value is higher than the original, the “decrease” becomes negative. That indicates an increase rather than a decrease.
• Results are shown to two decimals for consistency. For quick mental checks, you can round the percent to the nearest whole number.
• This tool measures a single change from one point to another. For multiple changes over time, calculate each step or use a time-series tool.

Common questions

What is the formula for percentage decrease?

The percentage decrease is calculated as: (original minus new) divided by original, multiplied by 100. In symbols: % decrease = ((Original − New) ÷ Original) × 100. The decrease amount is simply Original − New.

Why does the original value matter so much?

Because the percentage is measured relative to where you started. A drop of 50 units can be a small change or a huge change depending on the original. Dropping from 1,000 to 950 is only a 5% decrease. Dropping from 200 to 150 is a 25% decrease, even though the amount is still 50.

What if the new value is bigger than the original?

Then you do not have a decrease. Mathematically, the difference (original − new) becomes negative, so the percentage decrease becomes negative as well. This calculator will still show the numbers, but interpret a negative “decrease” as an increase. If you want a more direct “increase” label, use a percentage increase calculator instead.

Is percentage decrease the same as “percent off” for discounts?

In most shopping contexts, yes. If an item was 500 and is now 400, the percent off is ((500 − 400) ÷ 500) × 100 = 20% off. The same math applies to any kind of reduction, not only prices.

How do I calculate a percent decrease quickly without a calculator?

First estimate the difference, then compare it to the original. For example, from 250 down to 200 is a drop of 50. Since 25 is 10% of 250, 50 is 20%. For harder numbers, estimate using benchmarks like 1%, 5%, 10%, 25%, and 50% of the original.