Business Finance
Percentage Change Calculator
Find the percentage increase or decrease from an old value to a new one. Compare the absolute change, see the calculation and understand what a negative or zero starting value means.
Your comparison
Ready when you areA change of 20. An increase of 25%.
The starting value is the comparison base. Enter your own numbers to see both the amount and percentage of change.
(New − old) ÷ |old| × 100
The method
How to calculate percentage change
Subtract the old value from the new value to find the absolute change. For a positive starting value, divide that change by the old value and multiply by 100. A positive result means the number increased; a negative result means it decreased. The order matters because the old value supplies the comparison base. For a negative starting value, this tool divides by its absolute value and labels that convention beside the result.
Example 1
From 80 to 100: a 25% increase
The amount rises by 20. Relative to the original 80, the calculation is 20 ÷ 80 × 100 = 25%. Reversing the comparison gives a 20% decrease: (80 − 100) ÷ 100 × 100 = −20%. A rise and its reversal do not use the same denominator.
- Old value
- 80
- New value
- 100
- Change
- +25%
Example 2
A drop from 100 to zero
The absolute change is −100. Dividing by the original 100 gives −100%, a complete reduction of a positive starting amount. Starting at zero is a different case: division by zero cannot give a finite relative percentage.
- Old value
- 100
- New value
- 0
- Change
- −100%
Example 3
Negative starting values need a convention
From −100 to −50, the number rises by 50. Relative to the starting magnitude of 100, this tool reports +50%. From −50 to +50, the absolute rise is 100 and the magnitude-based change is +200%. That second example crosses zero; neither result should be presented as a universal accounting growth rate or investment return.
- Old value
- −100
- New value
- −50
- Magnitude-based change
- +50%
Before you calculate
Assumptions & limits
- Compare quantities in the same unit with a meaningful starting baseline. This is a numerical comparison, not a forecast, compound-growth model, investment return or professional valuation.
- Inputs support up to six decimal places and values from −1,000,000,000,000 to +1,000,000,000,000. Use a decimal point without grouping commas, percent signs or scientific notation.
- A negative old value uses its absolute magnitude as the denominator. Other fields may use different conventions; the interpretation is disclosed beside affected results.
- When the old value is zero, relative percentage change is undefined. The absolute change is still valid. Zero to zero means no absolute change, but does not create a defined percentage.
- Exact decimal inputs are used before rounding percentages to six decimals, halfway away from zero. Tiny nonzero percentages are displayed as a bound. Absolute changes retain all entered decimal precision.
- Swapping or editing values clears the previous answer. Values are calculated in your tab without saving them or including them in URLs or analytics.
Keep in mind
Common mix-ups
An increase and its reverse are not symmetric
A 25% increase takes 80 to 100. A 25% decrease from 100 takes it to 75, not 80. To return from 100 to 80, the decrease is 20%, because the starting base is now 100.
Percentage points describe changes in rates
A rate rising from 20% to 25% gains five percentage points. Relative to the original rate, it rises by 25%. Entering 20 and 25 here calculates that relative percentage change; this tool does not label it as five percent.
Percentage difference has a different baseline
For two positive measurements with no old/new order, a common percentage-difference method divides their absolute gap by their mean. For 80 and 100 it gives about 22.222222%. This calculator instead uses the starting value, so those same ordered inputs give +25%.
A large percentage can start from a tiny base
Going from 0.01 to 1 gives a 9,900% increase, while the absolute change is 0.99. Read both results together. Large percentages alone do not establish business importance or a reliable trend.
Sources & calculation notes
Reference for directional change and the explicitly stated absolute-start-value denominator. BiznTools independently checks its worked examples and edge cases.
Independent reference for the magnitude convention and the distinction between initial and final values; not an endorsement of BiznTools.
Calculation and input rules checked: . Engineering validation; no professional accounting review is claimed.