Percentage Change Calculator
Enter an original value and a new value to find the percentage increase or decrease.
Apply a Percentage Increase or Decrease
Use this tool when you know the starting value and the percentage change.
How to Calculate Percentage Increase or Decrease
A percentage increase or decrease calculator helps you quickly measure how much something changed compared to its original value. This is useful for prices, salaries, stock values, expenses, body weight, grades, and almost any situation where numbers go up or down over time.
The core idea is simple: you compare the difference between two numbers to the original number, then convert that ratio into a percentage.
Formula for Percentage Change
Use this formula when you have an original value and a new value:
Percentage Change = ((New Value - Original Value) / Original Value) × 100
- 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.
Step-by-Step Example
Example 1: Increase
Suppose a monthly subscription price rises from 40 to 50.
- Difference = 50 - 40 = 10
- 10 / 40 = 0.25
- 0.25 × 100 = 25%
The subscription increased by 25%.
Example 2: Decrease
A product drops from 120 to 90.
- Difference = 90 - 120 = -30
- -30 / 120 = -0.25
- -0.25 × 100 = -25%
The product price decreased by 25%.
Applying a Known Percent Increase or Decrease
Sometimes you already know the percentage and want the final value. For example, “Increase 80 by 12%” or “Decrease 500 by 18%.”
- New value after increase = Original × (1 + Percent/100)
- New value after decrease = Original × (1 - Percent/100)
This is exactly what the second tool in the calculator does.
Common Mistakes to Avoid
- Using the new value as the denominator. The denominator should usually be the original value.
- Confusing percentage points with percent change. A move from 10% to 15% is a 5-point increase, but a 50% relative increase.
- Ignoring negative signs. A negative result means decrease.
- Trying to divide by zero. If the original value is zero, percentage change is undefined in standard terms.
Where This Calculator Is Useful
- Comparing monthly expenses and budgeting changes
- Tracking sales growth or decline in business reports
- Calculating salary raises or pay cuts
- Monitoring fitness progress like weight gain or loss
- Analyzing market movement in investing
- Reviewing academic performance across semesters
Quick FAQ
Can percentage decrease be more than 100%?
In normal real-world contexts with non-negative starting values, a decrease cannot exceed 100% without crossing below zero. In pure math with signed values, unusual results can occur depending on definitions.
What if the original value is zero?
Standard percentage change is undefined because you cannot divide by zero. In that case, describe the change in absolute terms instead.
Why do people get different answers for similar numbers?
Usually because they used different baselines. Always verify what is considered the original/reference value.
Final Thoughts
Understanding percentage increase and decrease makes decision-making clearer in finance, business, and daily life. Use the calculator above for fast, accurate results, then rely on the formulas when you need to explain your numbers to others.