Percentage Change Calculator
Enter an original value and a new value to calculate the percentage increase or decrease instantly.
If you've ever asked, "How do you calculate a percentage change?", you're not alone. This is one of the most useful calculations in everyday life and business. You use it when prices go up, when sales drop, when your weight changes, or when your investment grows.
The good news: percentage change is simple once you know the formula and the order of steps.
The Percentage Change Formula
To find percentage change, use this formula:
That's it. The sign of the answer tells you what happened:
- Positive result = percentage increase
- Negative result = percentage decrease
- Zero = no change
Step-by-Step: How to Calculate Percentage Change
1) Identify the original value and new value
The original value is your starting point. The new value is what it changed to.
2) Subtract original from new
This gives you the raw change (also called absolute change):
3) Divide by the original value
This converts the raw change into a relative change compared to where you started.
4) Multiply by 100
Now convert the decimal into a percentage.
Worked Examples
Example 1: Price increase
A product goes from $80 to $100.
- Change = 100 - 80 = 20
- Change ÷ Original = 20 ÷ 80 = 0.25
- 0.25 × 100 = 25%
Result: 25% increase.
Example 2: Sales decrease
Monthly sales go from 2,500 units to 1,800 units.
- Change = 1,800 - 2,500 = -700
- -700 ÷ 2,500 = -0.28
- -0.28 × 100 = -28%
Result: 28% decrease.
Example 3: No change
If a value stays at 45 and ends at 45:
- Change = 45 - 45 = 0
- 0 ÷ 45 = 0
- 0 × 100 = 0%
Result: 0% change.
| Original | New | Raw Change | Percentage Change |
|---|---|---|---|
| 80 | 100 | +20 | +25% |
| 2,500 | 1,800 | -700 | -28% |
| 45 | 45 | 0 | 0% |
Common Mistakes to Avoid
- Using the wrong denominator: divide by the original value, not the new value.
- Forgetting to multiply by 100: if your result is 0.15, the percentage is 15%.
- Mixing up increase and decrease: negative means decrease; positive means increase.
- Confusing percentage points with percent change: a move from 10% to 12% is a 2 percentage-point increase, but a 20% percent increase.
Percentage Change vs Percentage Difference
These are not the same thing:
- Percentage change compares a new value to an original baseline.
- Percentage difference compares two values symmetrically, often using their average.
If you care about "before vs after," use percentage change.
What If the Original Value Is Zero?
When the original value is 0, the standard percentage change formula breaks because division by zero is undefined.
Quick Mental Math Tips
For a percentage increase
If something rises by 10 from 50, that is 10 ÷ 50 = 0.2 = 20% increase.
For a percentage decrease
If something drops by 15 from 60, that is 15 ÷ 60 = 0.25 = 25% decrease.
Reverse checks
After calculating, sanity-check your answer. A small absolute change from a small base can produce a large percentage change.
Where Percentage Change Is Used
- Stock returns and investment performance
- Revenue and profit analysis
- Website traffic and conversion rates
- Population growth or decline
- Weight, fitness, and health metrics
- Inflation and cost-of-living changes
FAQ
Can percentage change be greater than 100%?
Yes. If a value more than doubles, the increase exceeds 100%.
Why is my result negative?
A negative result means the new value is lower than the original value (a decrease).
Should I round my answer?
Usually yes—two decimal places is common in business and reporting.
Final Takeaway
To calculate percentage change, subtract the original value from the new value, divide by the original, and multiply by 100. Once you practice this a few times, it becomes second nature.
Use the calculator above whenever you want a fast answer, and use the steps in this article when you want to show your work clearly.