Percentage Decrease Calculator
Calculate percentage decrease from a positive original value to a nonnegative value no greater than the original. See examples and a two-decimal result.
Formula: Percentage decrease = ((original − new) ÷ original) × 100%
Enter a positive original value and a new value from 0 up to the original. Select Calculate; the result is rounded to two decimal places.
The Percentage Decrease Calculator measures how much a nonnegative value has fallen relative to a positive original value. Enter the original and new values, select Calculate, and the widget returns the decrease as a percentage. It uses a fixed arithmetic formula, not AI.
The supported domain is deliberate: the original value must be greater than 0, and the new value must be between 0 and the original value, inclusive. An unchanged value is valid and produces a 0% decrease. A new value of 0 produces the maximum supported decrease of 100%. If the new value is higher than the original, use the Percentage Change Calculator instead of interpreting a negative result as a decrease.
How to Use the Percentage Decrease Calculator
- Enter a positive number in Original Value.
- Enter a nonnegative number in New Value. It may equal, but cannot exceed, the original.
- Select Calculate.
- Read the percentage decrease, displayed to two decimal places.
The form starts with 200 and 150. Selecting Calculate returns 25%. The initial result remains an em dash until you calculate. Changing either input clears the previous result, so select Calculate again after an edit. Invalid values produce a field-specific message linked to the relevant input.
Percentage Decrease Formula and Examples
Percentage decrease = ((original − new) ÷ original) × 100%First subtract the new value from the original. Divide that decrease by the original value, then multiply by 100. This follows the percent-decrease method in OpenStax’s percent applications guidance.
For 200 decreasing to 150, the decrease is 50 and (50 ÷ 200) × 100 = 25%. For 90 decreasing to 75, the exact value is about 16.6667%, which the interface displays as 16.67%. For 80 remaining at 80, the decrease is 0 and the result is 0%. For 80 decreasing to 0, the result is 100%.
Input Limits, Rounding and Related Calculators
Zero cannot be the original value because the formula divides by the original; division by zero does not define a percentage decrease. Negative inputs are outside this calculator’s supported comparison model. The calculation uses standard JavaScript number arithmetic, and the displayed result is rounded to two decimal places. That display precision does not prove that an input or business interpretation is correct.
Use the Percentage Change Calculator when you need one tool for either an increase or decrease. Use the Reverse Percentage Calculator to recover an original value, the Percentage Difference Calculator for a symmetric comparison without an original-value direction, or the Proportion Calculator for an equality between two ratios.
Frequently asked questions
How do I calculate percentage decrease?
Subtract the new value from the original value, divide the decrease by the positive original value, and multiply by 100.
What values does this calculator accept?
The original value must be greater than 0. The new value must be 0 or greater and no greater than the original value.
Why can’t the original value be zero?
The formula divides by the original value. Division by zero is undefined, so zero cannot be used as the original value.
What if the new value equals or exceeds the original?
An equal value is valid and returns a 0% decrease. A higher value is rejected; use a percentage increase or change calculator for that comparison.
Can the supported percentage decrease exceed 100%?
No. With a positive original value and a nonnegative new value, 100% is the maximum and occurs when the new value is 0.
How are results rounded?
The calculator uses standard JavaScript number arithmetic and displays the result rounded to two decimal places.
Does the result update automatically?
No. Select Calculate after entering both values. Changing either input clears the previous result until you calculate again.