Percentages show up everywhere — a salary hike, a price drop, an exam score — and the three most common percentage calculations all follow simple, fixed formulas once you know them.
Percentage of a number
(Percentage ÷ 100) × Number. What is 20% of 450? (20 ÷ 100) × 450 = 90.
Percentage increase
((New value − Old value) ÷ Old value) × 100. A salary moving from ₹40,000 to ₹46,000 is a ((46,000 − 40,000) ÷ 40,000) × 100 = 15% increase.
Percentage decrease
Same formula — the result is simply negative when the new value is lower. A price dropping from ₹2,000 to ₹1,700 is a ((1,700 − 2,000) ÷ 2,000) × 100 = −15%, i.e. a 15% decrease.
What percentage is X of Y
(Part ÷ Total) × 100. Scoring 42 out of 50 on a test is (42 ÷ 50) × 100 = 84%.
A common mistake
People often calculate a percentage increase and then apply the same percentage decrease expecting to return to the original number — it doesn’t work, because the base changes. A 20% increase from 100 gives 120; a 20% decrease from 120 gives 96, not 100.
Skip the manual arithmetic with the free Percentage Calculator — or if you’re specifically working out a sale price, the Discount Calculator is built for exactly that.