Percentage Change Calculator
Enter an original value and a new value to calculate the percentage increase or decrease.
What is percentage change?
Percentage change tells you how much a value has gone up or down compared to where it started. It is one of the most useful quick calculations in personal finance, business, data analysis, and everyday decisions.
For example, if your electricity bill rises from $120 to $150, percentage change tells you the size of that increase relative to the original $120.
The formula
The standard formula is:
- If the result is positive, it is a percentage increase.
- If the result is negative, it is a percentage decrease.
- If the result is 0, there is no change.
How to calculate percentage change in 3 steps
- Find the difference: New Value - Old Value
- Divide by the old value: Difference / Old Value
- Convert to percent: Multiply by 100
Example: Increase
Old value = 80, New value = 100
This is a 25% increase.
Example: Decrease
Old value = 200, New value = 150
This is a 25% decrease.
Where percentage change is useful
- Budgeting: Track rent, grocery, and utility increases year over year.
- Investing: Measure gains or losses in stocks, funds, or portfolios.
- Business: Compare monthly sales, conversion rates, or customer counts.
- Health and fitness: Evaluate bodyweight or performance improvements.
- Education: Compare test scores over time.
Percentage change vs. percentage points
These are often confused:
- Percentage points are absolute differences between percentages (e.g., 8% to 10% = +2 percentage points).
- Percentage change is relative (e.g., from 8% to 10% is a 25% increase because 2/8 = 0.25).
Use percentage points when comparing rates directly. Use percentage change when comparing relative growth or decline.
Common mistakes to avoid
1) Dividing by the wrong number
The denominator should usually be the old (starting) value, not the new one.
2) Ignoring the sign
A negative result means decrease. A positive result means increase.
3) Forgetting the zero rule
If old value is 0, percentage change is undefined because division by zero is not possible. In that case, report an absolute change instead.
Practical mini-examples
Salary
If salary rises from $60,000 to $66,000, the increase is ((66,000 - 60,000) / 60,000) × 100 = 10%.
Discount pricing
If a product drops from $40 to $30, percentage change is ((30 - 40) / 40) × 100 = -25%, meaning a 25% discount.
Website traffic
If visits increase from 12,000 to 15,600, percentage change is ((15,600 - 12,000) / 12,000) × 100 = 30%.
Final thoughts
Knowing how to calculate percentage change helps you make smarter decisions quickly. Whether you're reviewing expenses, evaluating performance, or comparing trends, this one formula gives clear context that raw numbers alone do not.
Use the calculator above anytime you need a fast, accurate percentage increase or decrease.