Five calculations, one tool
- X% of Y — the basic one. 18% of ₹2,500 is ₹450.
- X is what percent of Y — for shares and ratios. 45 out of 300 is 15%.
- Percentage change — for growth and decline between two periods.
- Increase by X% — adding a markup, a hike or a tax.
- Decrease by X% — applying a discount or a cut.
The formulas
X as a percent of Y = X ÷ Y × 100
Percentage change = ( New − Old ) ÷ |Old| × 100
Increase Y by X% = Y × ( 1 + X/100 )
Decrease Y by X% = Y × ( 1 − X/100 )
The percentage-point trap
If your conversion rate moves from 2% to 3%, that is a rise of one percentage point — and a 50% increase. Both statements are true and they mean very different things. Reports that mix the two are a reliable way to make a modest improvement sound like a breakthrough.
Increases and decreases do not cancel
Add 20% to ₹1,000 and you get ₹1,200. Take 20% off ₹1,200 and you get ₹960, not ₹1,000. The second percentage was applied to a larger base. This is the same arithmetic that makes reverse GST a division rather than a subtraction.
Frequently asked questions
How do I calculate percentage increase?
Subtract the old value from the new one, divide by the old value, and multiply by 100. Going from 200 to 250 is a 25% increase.
What is the difference between percent and percentage points?
Percentage points measure the absolute gap between two percentages. Percent measures the relative change. From 2% to 3% is one percentage point and a 50% increase.
Why does adding then removing the same percentage not return the original number?
Because the second calculation runs on a different base. The increase was applied to the smaller number and the decrease to the larger one.