Percentage Calculator
The four percentage questions everyone asks, each answered instantly: percent of a number, share as a percent, percent change, and increase or decrease by a percent.
The four percentage formulas
Nearly every percentage question in daily life reduces to one of four patterns, and mixing them up is the most common source of wrong answers.
2) X as % of Y = X ÷ Y × 100
3) % change = (New − Old) ÷ Old × 100
4) Y increased by X% = Y × (1 + X÷100)
The classic trap: percent change is not symmetric
A 20% fall followed by a 20% rise does not bring you back. ₹100 falling 20% becomes ₹80; rising 20% from there gives ₹96. The percentage is always measured against the starting value, which changed. This is why a stock that drops 50% needs a 100% gain to recover, and why calculator 3 above always asks which value is the old one.
Percentage points vs percent
If an interest rate moves from 8% to 10%, it rose 2 percentage points but 25 percent. News reports mix these up constantly. Use calculator 3 with 8 and 10 to see the 25% figure; the point difference is simple subtraction.
Everyday examples
Calculator 1 answers discount and tax questions: 18% of ₹2,500 is ₹450. Calculator 2 converts marks to percentages: 45 out of 60 is 75%. Calculator 3 measures growth: revenue moving from ₹80 lakh to ₹1 crore is a 25% increase. Calculator 4 applies a hike or a cut: a ₹1,200 bill with a 15% service charge becomes ₹1,380.
Reverse percentages: the shop-discount trap
A jacket costs ₹3,400 after a 15% discount; what was the original price? The wrong answer is 3,400 + 15% = ₹3,910. The right method divides: 3,400 ÷ 0.85 = ₹4,000, because the 15% was taken from the original price, not the discounted one. Use calculator 4 in reverse to check: ₹4,000 decreased by 15% is exactly ₹3,400. The same logic applies to prices quoted after tax, salaries quoted after deductions, and "net of fees" investment values.
Stacked percentages do not add
A 20% discount followed by an extra 10% off is not 30% off; it is 0.8 × 0.9 = 0.72 of the price, a 28% total discount. Similarly GST on a marked-up price compounds with the markup. Whenever two percentages apply one after another, multiply the factors instead of adding the rates; calculator 4 applied twice reproduces the correct result and shows how much the naive addition overstates the change.
Frequently asked questions
How do I calculate the percentage of a number?
Multiply the number by the percent and divide by 100. For example, 18% of 2,500 = 2,500 × 18 ÷ 100 = 450. Calculator 1 above does this instantly.
How do I work out percentage change?
Subtract the old value from the new value, divide by the old value, and multiply by 100. Going from 80 to 100 is (100−80)÷80×100 = +25%. Always divide by the value you started from.
Why doesn’t a 10% drop then a 10% rise return to the original?
Because each percentage applies to a different base. 100 drops to 90, then 10% of 90 is only 9, so you end at 99. The larger the swing, the bigger the gap.
What is the difference between percent and percentage points?
Points measure the simple difference between two percentages; percent measures the relative change. A rate going from 8% to 10% is up 2 points but up 25 percent.