Your result
What your result means
Going from 80 to 92 is an increase of 15% ((92 − 80) ÷ 80 × 100).
The math
Formula and sources
A% of B = A ÷ 100 × B A as % of B = A ÷ B × 100 % change A → B = (B − A) ÷ |A| × 100
- A
- first value (the percent, the part, or the starting value)
- B
- second value (the base, the whole, or the new value)
Percent change is measured against the starting value, so a rise from 100 to 125 (+25%) and a fall from 125 to 100 (−20%) are not the same size.
Sources we checked this against
- 1Calculating percent changesU.S. Bureau of Labor Statistics · bls.gov
- 2How to use the Consumer Price Index for escalationU.S. Bureau of Labor Statistics · bls.gov
Formula last checked 2026-11-04. Found an error? Tell us and we will fix it.
Step by step
Two worked examples
BLS: 12-month CPI change
Answer
6.4544%
- What do you want to find?
- Percent change from A to B
- A
- 278.802
- B
- 296.797
The BLS shows CPI-U rising from 278.802 (Dec 2021) to 296.797 (Dec 2022): 17.995 ÷ 278.802 × 100 = 6.4544%, published as 6.5%.
Sales tax on a purchase
Answer
46.4
- What do you want to find?
- What is A% of B?
- A
- 7.25
- B
- 640
7.25% of $640: 7.25 ÷ 100 × 640 = 46.4.
| Result | Example 1 | Example 2 |
|---|---|---|
| Answer | 6.4544% | 46.4 |
Questions
Frequently asked questions
What is the difference between percent and percentage points?
If a rate goes from 4% to 5%, it rose 1 percentage point, but 25 percent (1 ÷ 4). News reports on interest rates usually mean percentage points.
How do I reverse a percent increase?
Divide by (1 + the increase). A price that rose 20% to $60 was $60 ÷ 1.2 = $50 before — not $60 minus 20%.
Why can’t I calculate a percent change from zero?
Percent change divides by the starting value, and division by zero is undefined. Describe the change in absolute terms instead.