Percentage Decrease Formula: How to Calculate a Decrease

Percentage decrease measures how much a value has fallen relative to its original value. It is useful for price reductions, declining revenue, lower costs, shrinking quantities, performance changes, and many other before-and-after comparisons.

The basic formula is:

Percentage decrease = ((Original value − New value) ÷ Original value) × 100

If a value falls from 100 to 80, the decrease is 20 and the percentage decrease is 20%.

For a quick calculation, use the Percentage Decrease Calculator.

Percentage decrease formula

Start with two values:

• Original value: the starting or earlier value.
• New value: the value after the decrease.

Then follow three steps:

1. Subtract the new value from the original value.
2. Divide the decrease by the original value.
3. Multiply by 100 to convert the result to a percentage.

In formula form:

((Original − New) ÷ Original) × 100

The original value matters because it is the baseline. Percentage change answers the question: “How large was the change compared with where we started?”

Example: from 100 to 80

Suppose a monthly expense falls from $100 to $80.

1. Find the decrease: 100 − 80 = 20
2. Divide by the original value: 20 ÷ 100 = 0.20
3. Convert to a percentage: 0.20 × 100 = 20%

The expense decreased by 20%.

Example: price decrease

A product originally costs $250 and later sells for $200.

((250 − 200) ÷ 250) × 100 = 20%

The price decreased by 20%.

Notice that the dollar decrease is $50, while the percentage decrease is 20%. The percentage makes it easier to compare changes across items with different starting prices.

Example: revenue decline

Revenue falls from $120,000 to $102,000.

The absolute decrease is:

120,000 − 102,000 = 18,000

The percentage decrease is:

18,000 ÷ 120,000 × 100 = 15%

Revenue therefore decreased by 15%.

If you are comparing business revenue across periods, the Revenue Growth Calculator can show the same change as a negative growth rate.

Percentage decrease vs percentage increase

Percentage decrease and percentage increase use the same baseline principle: both divide the change by the original value.

• Increase: ((New − Original) ÷ Original) × 100
• Decrease: ((Original − New) ÷ Original) × 100

The Percentage Increase Calculator is useful when the new value is higher than the original value.

A 20% decrease followed by a 20% increase does not return to the starting value because the second calculation uses a smaller baseline. For example, 100 decreased by 20% becomes 80; increasing 80 by 20% gives 96.

Percentage decrease vs percentage difference

These terms answer different questions.

Percentage decrease compares a new value with a known original baseline. The original value is the denominator.

Percentage difference is usually used when neither value is naturally the baseline. It often divides the absolute difference by the average of the two values.

Use percentage decrease when you have a clear “before” and “after” relationship.

How to find the new value after a percentage decrease

Sometimes you know the original value and the percentage decrease but not the new value.

Use:

New value = Original value × (1 − Decrease percentage ÷ 100)

For example, to reduce 500 by 12%:

500 × (1 − 0.12) = 440

The new value is 440.

This is the same structure used by the Discount Calculator when calculating a sale price.

How to find the original value after a decrease

If you know the new value and the percentage decrease, rearrange the formula:

Original value = New value ÷ (1 − Decrease percentage ÷ 100)

If a value is 160 after a 20% decrease:

160 ÷ 0.80 = 200

The original value was 200.

Common percentage decrease mistakes

Using the new value as the denominator

The baseline should normally be the original value. Dividing by the new value answers a different question and produces a different percentage.

Confusing percentage points with percent change

If a rate falls from 40% to 30%, it fell by 10 percentage points. Relative to the original 40%, however, the percentage decrease is 25%.

Ignoring a zero original value

The standard percentage-change formula cannot use an original value of zero because division by zero is undefined. In that case, report the absolute change or use another metric that fits the context.

Treating every negative result as a decrease

If you enter a new value greater than the original into a decrease formula, the result becomes negative. That usually means the change was actually an increase.

When percentage decrease is useful

Percentage decrease is especially helpful when comparing changes across different scales. Examples include:

• a reduction in product price;
• a decline in monthly costs;
• a decrease in website traffic;
• lower defect or error counts;
• a reduction in inventory;
• declining revenue or units sold.

Always keep the comparison period and measurement definition consistent. A monthly value compared with an annual value, for example, does not produce a meaningful change rate without adjustment.

FAQ

What is the percentage decrease from 80 to 60?

The decrease is 20. Divide 20 by the original value of 80 and multiply by 100: 20 ÷ 80 × 100 = 25%. The percentage decrease is 25%.

What is a 30% decrease from 200?

Multiply 200 by 70%, because 100% − 30% = 70%: 200 × 0.70 = 140. The new value is 140.

Can percentage decrease be more than 100%?

For ordinary non-negative quantities where the new value cannot fall below zero, a decrease from a positive starting value reaches 100% when the new value reaches zero. Contexts that allow negative values can behave differently, so interpret the result according to the metric being measured.

Is percentage decrease the same as discount percentage?

A discount percentage is a specific use of percentage decrease applied to price. The underlying arithmetic is the same when the original price is the baseline.

Calculate your percentage decrease

Enter the original and new values in the Percentage Decrease Calculator to get the result instantly, then use the examples above to interpret the change correctly.