Calculators guide
How to Calculate Percentage Increase (and Decrease) — With Examples
The one formula for percentage increase and decrease, worked examples with prices and salaries, and the mistakes that trip people up — like percent vs percentage points.
By M2Toolkit Editorial TeamPublished 6 min read
Quick answer
Percentage increase = (new value − old value) ÷ old value × 100.
From 80 to 100: (100 − 80) ÷ 80 × 100 = 25%. If the answer is negative, it's a decrease: from 100 to 80 is −20%. The Percentage Change Calculator does this instantly and shows the working.
The formula fits on one line, yet percentage changes are misreported all the time — in sales reports, news headlines and “50% off” signs. The math is rarely the problem. Mistakes come from dividing by the wrong number, mixing up percent and percentage points, and assuming percentages add up.
Step by step
- 1Subtract the old value from the new value. That's the change.
- 2Divide the change by the old value — the one you started from.
- 3Multiply by 100.
Example: a website had 950 visitors last month and 1,200 this month. The change is 250. 250 ÷ 950 = 0.263, so traffic grew by about 26.3%.
Try the free Percentage Change CalculatorEnter the old and new values; see the percentage change, difference and multiplier.Percentage decrease uses the same formula
A price drops from $60 to $45. The change is −15; −15 ÷ 60 = −0.25, so it's a 25% decrease. Some people prefer to write it as a positive number with the word “decrease”:
Why going up and coming back down aren't the same
80 → 100 is +25%, but 100 → 80 is −20%. Same two numbers, different percentages, because each calculation divides by a different starting value. It matters most for successive changes:
| Start | First change | Then | Result | Overall |
|---|---|---|---|---|
| 100 | +10% | −10% | 99 | −1% |
| 100 | −50% | +50% | 75 | −25% |
| 100 | +20% | +20% | 144 | +44% (not 40%) |
To combine changes, multiply the factors: +20% then +20% is 1.2 × 1.2 = 1.44, a 44% increase.
Percent vs percentage points
If an interest rate rises from 4% to 5%, it went up by 1 percentage point — but by 25 percent (1 ÷ 4). Both statements are true; they answer different questions. When the values are themselves percentages, say “points” for the simple difference.
In Excel or Google Sheets
With the old value in A1 and the new value in B1, use =(B1-A1)/A1 and format the cell as a percentage. To reverse it — find the original from a new value and a known percentage increase — use =B1/(1+C1), where C1 holds the percentage.
Frequently asked questions
Can a percentage increase be more than 100%?
Yes. Going from 50 to 150 is a 200% increase. A value that doubles has increased by 100%.
What if the old value is zero?
The percentage change is undefined — you can't divide by zero. Report the absolute change instead (for example, “up from 0 to 40”).
What's percentage difference?
It compares two values without treating either as the starting point: |A − B| ÷ average(A, B) × 100. The Percentage Change Calculator shows it too.