Everyday maths
Percentage increase and decrease: calculate the change with examples
Use the original value as the reference point to calculate a percentage increase or decrease correctly.
Updated July 30, 2026 · 4 min read
Use the original value as the baseline
Percentage change compares a new number with the value it started from. Subtract the original value from the new value, divide the difference by the original value, and multiply by 100.
For example, a price rising from Rs. 800 to Rs. 920 changes by Rs. 120. Divide 120 by 800 and multiply by 100 to get a 15% increase.
A decrease uses the same reference point
For a decrease, the new number is lower than the original one. A price dropping from Rs. 800 to Rs. 680 changes by minus Rs. 120, which is a 15% decrease when you divide by the original Rs. 800.
The denominator matters. Dividing by the new value instead of the original value answers a different question and can make the percentage look larger or smaller than it should.
Do not add or reverse percentage changes blindly
A 20% decrease followed by a 20% increase does not return to the starting value. The increase is calculated from the lower number, so the two percentage changes use different baselines.
Use a calculator for the exact result when you compare marks, prices, traffic, revenue, or performance metrics. Keep the original and final values beside the percentage so the result stays understandable.
Put this guide into practice
Use the related calculators
Put the steps in this guide into practice with a focused calculator, then return here to check an assumption or compare another scenario.