A percentage decrease calculator measures how much a value has shrunk from its starting point, expressed as a percentage rather than a raw number. That distinction matters because a $20 drop means something very different depending on whether the original price was $40 or $4,000 — the percentage decrease is what makes those two situations comparable. For a part-to-whole percentage instead, use the percentage calculator.
This page covers how to calculate percentage decrease using the standard formula, walks through several worked examples, and explains how the exact same calculation doubles as a percentage off calculator for retail discounts — since "20% off" and "a 20% decrease" describe the same math. A working percent decrease calculator is available above for anyone who wants the instant result without doing the arithmetic manually. Browse all calculators if you need a different tool.
How to Calculate Percentage Decrease: The Formula
The Percentage Decrease Formula
The formula for calculating percentage decrease is:
Percentage Decrease = ((Old Value − New Value) ÷ Old Value) × 100
The "Old Value" is the starting point, the "New Value" is where the number ended up after the decrease, and dividing the difference by the original value expresses how large the drop was relative to where it started. This is the exact calculation people mean when they search for how to calculate percentage decrease or calculate percentage decrease more generally.
Note that this formula is the mirror image of the percentage increase formula — the only difference is which value comes first in the subtraction, since a decrease is being measured as a positive percentage rather than expressed as a negative increase.
Worked Examples: Percentage Decrease in Practice
Example: Price Dropping From $80 to $60
Old Value = 80, New Value = 60
(80 − 60) ÷ 80 = 0.25
0.25 × 100 = 25% decrease
A price falling from $80 to $60 represents a 25% decrease.
Example: Weight Reducing From 90kg to 81kg
Old Value = 90, New Value = 81
(90 − 81) ÷ 90 = 0.10
0.10 × 100 = 10% decrease
A weight change from 90kg to 81kg is a 10% decrease — a common way this calculation is used when tracking progress toward a health or fitness goal over time.
Example: Sales Falling From 500 Units to 425 Units
Old Value = 500, New Value = 425
(500 − 425) ÷ 500 = 0.15
0.15 × 100 = 15% decrease
A drop from 500 units sold to 425 units sold represents a 15% decrease — a figure that's far more useful for reporting and comparison than the raw 75-unit difference on its own.
Using This as a Percentage Off Calculator for Discounts
Calculating a Percentage Off Price
"Percentage off" and "percentage decrease" describe the same underlying calculation — a discount is simply a decrease applied to a price. If an item originally costs $50 and is marked 30% off, the calculation works in reverse from the decrease formula above:
Discounted Price = Old Value × (1 − Percentage ÷ 100)
For a $50 item at 30% off: 50 × (1 − 0.30) = 50 × 0.70 = $35
Working Out What a Discount Actually Saves
The other common version of this question is figuring out what percentage a sale price represents as a discount from the original. If an item was $80 and is now selling for $60, that's the same calculation as the worked example above — a 25% decrease, or equivalently, 25% off the original price. This percentage off calculator use case is one of the most frequent real-world applications of the percentage decrease formula, since retail pricing, sales, and clearance tags are built around exactly this number.
Where a Percent Decrease Calculator Is Used
Retail & Discount Pricing
Working out the final price after a percentage-off discount, or checking what percentage a sale price represents compared to the original listed price.
Budget & Expense Reduction
Measuring how much a budget, department cost, or personal expense has been reduced compared to a previous period, expressed as a clean percentage for reporting or comparison.
Weight Loss & Health Tracking
Tracking percentage decrease in body weight, resting heart rate, or other health metrics over time, since percentage change is often more meaningful for progress tracking than the raw number alone.
Percentage Decrease vs. Percentage Increase vs. Percentage Difference
These three calculations are related but not interchangeable. Percentage decrease measures a directional drop from a starting value to a lower ending value — this calculator. Percentage increase measures the opposite direction, a rise from a starting value to a higher one, handled by the percentage increase calculator. Percentage difference is different from both — it's a symmetrical comparison between two values with no assumed direction or starting point, handled by the percentage difference calculator.
Choosing the wrong one of these three for a given question will still produce a number, but it may not be the number that actually answers the question being asked — particularly with percentage difference, which produces a different result from percentage decrease even when applied to the exact same two figures.
Common Mistakes to Avoid
Dividing by the new value instead of the old value. The percentage decrease formula divides by the original (old) value — dividing by the smaller, new value instead will produce an inflated, incorrect percentage.
Confusing "percentage off" with the final price. A 30% off calculation gives the amount saved as a percentage, not the final price directly — the final price requires the additional step of subtracting that percentage from the original value (or multiplying by the remaining percentage, as shown above).
Stacking discounts incorrectly. Two sequential discounts (like 20% off, then an additional 10% off) don't simply add up to 30% off — each percentage decrease applies to the already-reduced price, so the combined effect is slightly less than a flat 30%.
Frequently Asked Questions
How do I calculate percentage decrease?
Subtract the new value from the old value, divide the result by the old value, then multiply by 100. For example, going from 80 to 60 is ((80 minus 60) divided by 80) times 100, which equals a 25% decrease.
What's the formula for percentage decrease?
Percentage Decrease equals (Old Value minus New Value) divided by Old Value, multiplied by 100.
How do I use this as a percentage off calculator?
Enter the original price and the discount percentage. The discounted price is calculated as Old Value multiplied by (1 minus Percentage divided by 100). For a $50 item at 30% off, that equals $35.
What is the percentage decrease from 90 to 81?
That is a 10% decrease, calculated as ((90 minus 81) divided by 90) times 100.
Is percentage off the same as percentage decrease?
Yes. A percentage off discount and a percentage decrease describe the same mathematical operation: reducing a value by a set percentage of itself.
How do two discounts stack, like 20% off and then 10% off?
They do not simply add to 30% off. Each discount applies to the already-reduced price, so 20% off followed by 10% off results in a combined discount of 28%, not 30%.
Is percentage decrease the same as percentage difference?
No. Percentage decrease measures a directional drop from a starting value to an ending value. Percentage difference is a symmetrical comparison between two values with no assumed direction, and typically produces a different result.
Is this percent decrease calculator free to use?
Yes. It is free, requires no sign-up, and returns results instantly as values are entered.