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.