calculate decrease by percentage

How to Calculate a Decrease by Percentage

If you want to reduce a number by a certain percent, the process is simple once you know the formula. This is useful for sale prices, budget cuts, investment drops, depreciation, and performance tracking.

A percentage decrease tells you how much something went down relative to its original amount. The key is that percent is always based on the starting value, not the ending value.

The Core Formula

To decrease a value by a percentage:

• Decrease amount = Original Value × (Percentage ÷ 100)
• New value = Original Value − Decrease amount

You can also combine it into one line: New value = Original Value × (1 − Percentage ÷ 100).

Method 1: Reduce a Number by a Percentage

Example: Price Discount

A jacket costs $120 and is marked down by 25%.

• Decrease amount = 120 × 0.25 = 30
• New price = 120 − 30 = 90

The final price is $90.

Example: Budget Cut

A department budget is 80,000 and needs to be cut by 12%.

• Decrease amount = 80,000 × 0.12 = 9,600
• New budget = 80,000 − 9,600 = 70,400

The new budget is 70,400.

Method 2: Find the Percentage Decrease Between Two Values

Sometimes you already know the old and new numbers and want the percent decrease.

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

Example: Revenue Drop

Revenue moved from 50,000 to 42,500.

• Difference = 50,000 − 42,500 = 7,500
• Percentage decrease = (7,500 ÷ 50,000) × 100 = 15%

The business experienced a 15% decrease.

Reverse Calculation: Find the Original Value

If you know the new value and the percentage decrease, you can solve for the original:

• Original value = New Value ÷ (1 − Percentage ÷ 100)

Example: A value after a 20% decrease is 400. Original = 400 ÷ 0.80 = 500.

Common Mistakes to Avoid

• Using the wrong base: Always base the percent on the original value.
• Forgetting to divide by 100: 15% is 0.15, not 15.
• Subtracting percent directly: Don’t do 250 − 15 unless you mean 15 units, not 15%.
• Mixing increase and decrease formulas: A decrease subtracts; an increase adds.

Real-World Uses

Knowing how to calculate a decrease by percentage helps in many everyday situations:

• Shopping discounts and markdown pricing
• Salary or expense reductions
• Stock or portfolio drawdowns
• Website traffic and conversion declines
• Annual depreciation for assets

Quick Reference

• New after decrease: Original × (1 − p/100)
• Decrease amount: Original × p/100
• Percent decrease from two values: ((Original − New)/Original) × 100

Use the calculator above whenever you need a fast, accurate answer. It works for simple discounts and for deeper analysis where you compare before-and-after values.