Whether you’re analyzing sales growth, tracking price changes, or comparing test scores, knowing how to calculate percentage increase or decrease is an essential everyday skill. This guide covers every scenario with clear formulas and real examples.
Percentage Increase Formula
% Increase = (New Value − Old Value) ÷ Old Value × 100
Example: A product was $40 and is now $52.
% Increase = (52 − 40) ÷ 40 × 100 = 12 ÷ 40 × 100 = 30% increase
Percentage Decrease Formula
% Decrease = (Old Value − New Value) ÷ Old Value × 100
Example: Revenue dropped from $80,000 to $64,000.
% Decrease = (80,000 − 64,000) ÷ 80,000 × 100 = 16,000 ÷ 80,000 × 100 = 20% decrease
How to Calculate Percentage Change (Increase or Decrease)
The single universal formula works for both increases and decreases. A positive result means an increase; a negative result means a decrease.
% Change = (New − Old) ÷ |Old| × 100
Common Percentage Calculations You’ll Need
Finding a Percentage of a Number
Part = Percentage × Whole ÷ 100
Example: 15% of 200 = 15 × 200 ÷ 100 = 30
Finding What Percentage One Number Is of Another
% = Part ÷ Whole × 100
Example: 45 is what % of 180? → 45 ÷ 180 × 100 = 25%
Finding the Original Value Before a Percentage Change
Original = New Value ÷ (1 + % ÷ 100)
Example: After a 20% increase, the price is $60. What was the original? → 60 ÷ 1.20 = $50
Quick Reference: Common Percentage Changes
| Scenario | Old | New | Change |
|---|---|---|---|
| Salary raise | $50,000 | $55,000 | +10% |
| Product discount | $120 | $90 | −25% |
| Website traffic | 1,200 visits | 1,800 visits | +50% |
| Stock price drop | $250 | $200 | −20% |
Percentage Increase vs. Percentage Points
This distinction matters enormously in finance and statistics. If an interest rate goes from 2% to 3%, it increased by 1 percentage point — but it increased by 50% in relative terms. Always clarify which you mean to avoid confusion.
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