Percentage change measures how much a value has gone up or down relative to where it started: (new − old) / |old| × 100. A positive result is a percent increase, a negative one a percent decrease. From 100 to 150 is a +50% increase; from 80 to 60 is a −25% decrease.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: the percentage-change formula, recomputed in code.
The formula
Subtract the old value from the new value to get the raw change, divide by the old value (the base), and multiply by 100. Dividing by the old value is what makes it a change relative to the starting point. A positive percentage means it grew; a negative one means it shrank. The absolute difference is the same change in the original units.
Worked examples
An increase from 100 to 150:
A decrease from 80 to 60:
A drop from 200 to 170:
So 100 to 150 is a 50% increase, 80 to 60 is a 25% decrease, and 200 to 170 is a 15% decrease. Remember a 50% rise then a 50% fall lands at 75, not back at 100 — each percent is on a different base.
Frequently Asked Questions
(new − old) / |old| × 100. 100 → 150 = +50%. Positive is increase, negative is decrease.
Same formula, larger new value. 50 → 75 = +50% increase.
Same formula, smaller new value → negative. 80 → 60 = −25%, a difference of 20.
No. 100 → 150 → 75. Each percent is on a different base, so they don't cancel.
Change is old → new over time. Percent error is vs a true value. Percent difference has no reference.