Percentage Calculator

Four percentage problems, one page

Almost every percentage question you meet — exam marks, discounts, GST, salary hikes, population growth — is one of four calculations. Each card above handles one of them and updates as you type, so you can answer a question in seconds without remembering which number goes on top.

1. What is X% of Y?

Result = Y × X ÷ 100

Use this for discounts, tips, commission and tax. 15% of ₹2,400 is 2,400 × 15 ÷ 100 = ₹360. A faster mental method: 10% of 2,400 is 240, half of that (5%) is 120, so 15% is 240 + 120 = 360.

2. X is what percent of Y?

Percentage = X ÷ Y × 100

This turns marks or shares into a percentage. Scoring 45 out of 60 is 45 ÷ 60 × 100 = 75%. If a survey found 320 of 1,250 people prefer tea, that is 25.6%.

3. Percentage change from X to Y

Change = (Y − X) ÷ X × 100

A salary rising from ₹80,000 to ₹1,00,000 is a 25% increase. Note the direction matters: falling from ₹1,00,000 back to ₹80,000 is a 20% decrease, not 25%, because the base is now the larger number. This asymmetry is why a 50% loss needs a 100% gain to recover.

4. Discount and final price

Final price = Original × (1 − discount ÷ 100)

A ₹1,999 item at 30% off costs 1,999 × 0.70 = ₹1,399.30, saving ₹599.70. Enter a negative discount to compute a markup: −20% on a ₹500 cost price gives a ₹600 selling price.

Percentage points vs percent

If an interest rate moves from 6% to 8%, it rose by 2 percentage points but by 33.3 percent (2 ÷ 6). News reports mix these up constantly. Card 3 gives the percent change; the percentage-point difference is simply the subtraction.

Reverse percentages

To find the original value when you know the result after a percentage change, divide rather than multiply. If a phone costs ₹23,600 after 18% GST, the pre-tax price is 23,600 ÷ 1.18 = ₹20,000. If a stock is ₹150 after a 25% rise, it started at 150 ÷ 1.25 = ₹120. The GST calculator on this site handles the tax case directly.

Common mistakes

• Adding successive percentages: 20% off followed by 10% off is 28% off, not 30%, because the second discount applies to the reduced price.
• Averaging percentages from different-sized groups without weighting them.
• Forgetting that a percentage of a percentage is a multiplication: 50% of 40% is 20%.

Frequently asked questions