THE NUMORIX GUIDE
How to use the Percentage Change Calculator
Last reviewed September 14, 2026
What this calculator does
Subtract original from new value to get change, then divide by the original and multiply by 100: percentage change = (new - original)/original * 100.
Formula and method
Subtract original from new value to get change, then divide by the original and multiply by 100: percentage change = (new - original)/original * 100.
Variables and inputs
Original Value defaults to 100 and New Value to 150. The original cannot be zero because it is the denominator.
Worked example
From 100 to 150: change = 150 - 100 = 50; percentage change = 50/100 * 100 = +50%. If the new value were 80, the same formula would give -20%.
How to interpret the result
A positive result is an increase relative to the starting value; a negative result is a decrease relative to that starting value.
Common mistakes to avoid
Use the original value as the denominator, not the new value. Do not confuse percentage change with percentage-point change for percentages.
Assumptions and limitations
The formula is undefined at an original value of zero and can be unintuitive for negative originals. It does not account for compounding over multiple changes.
Practical use and checks
Percentage change measures a new value relative to an original value. Enter original 100 and new 150 as a check; the result should be +50%. Changing the new value to 80 should produce -20%, because the difference is -20 and the original reference is 100. Use the calculator for price, count, revenue, or measurement changes when the starting value is the meaningful baseline, and keep the sign because it tells whether the value rose or fell. Do not switch the denominator to the new value merely because it is easier to see. A fall from 100 to 50 is -50%, while a recovery from 50 to 100 is +100%; the direction and reference base are different. For rates such as 60% and 70%, distinguish a 10 percentage-point change from a 16.67% relative increase. An original value of zero makes the formula undefined, and negative originals can make the sign feel counterintuitive even when the arithmetic is valid. The tool measures one before-and-after change; it does not compound a sequence, adjust for inflation, or explain causation. Describe the reference period, units, and any rounding policy beside the percentage when using it in a report.