Percentage Calculator

A percentage is simply a number expressed as a fraction of 100 — the word comes from the Latin per centum, “per hundred”. Saying 18% is the same as saying 18 out of every 100. Percentages turn up everywhere in daily Indian life: exam marks and CGPA conversions, GST on a restaurant bill, a Flipkart or Myntra sale discount, the interest rate on a fixed deposit, a salary hike, the markup a shopkeeper adds, or the share of your income that rent eats up. This free percentage calculator handles the three questions that cover almost every real-world percentage problem — find a percentage of a number, work out what percentage one number is of another, or measure the change between two values — and shows the exact formula it used so you can learn the method, not just copy the answer.

Who this calculator is for

It is built for everyone who meets percentages in ordinary life: a student converting marks into a percentage or checking an aggregate across subjects; a shopper verifying a “flat 40% off” banner during a sale; a salaried professional sizing up an appraisal hike; a small-business owner or freelancer adding or removing GST and setting a markup; and an investor measuring the gain or loss on a stock, mutual fund, or FD. No formula memorisation is needed — pick a mode and read the result.

The three percentage formulas

1. What is X% of Y?  Result = (X / 100) × Y
Use this to find a part of a whole — GST on a price, a discount amount, a tip, a commission, or one year's simple interest.

2. X is what % of Y?  Result = (X / Y) × 100
Use this to express one number as a percentage of another — marks scored out of the total, attendance out of total classes, or one expense as a share of your income.

3. Percentage change from X to Y:  Result = ((New − Old) / |Old|) × 100
Use this for a salary hike, a price rise, or a portfolio gain or loss. A positive answer is an increase; a negative answer is a decrease.

Worked example — a sale bill in ₹

A jacket is listed at ₹2,000 with a 30% discount. The discount amount is (30 / 100) × 2,000 = ₹600 (mode 1), so the sale price is ₹1,400. If 18% GST then applies on ₹1,400, the GST is (18 / 100) × 1,400 = ₹252, making the final bill ₹1,652. To check what fraction of the original ₹2,000 you actually paid, switch to mode 2: (1,652 / 2,000) × 100 = 82.6% — so the “30% off” tag, once GST is added back, left you paying about 82.6% of the sticker price.

Worked example — exam marks

Say you scored 437 out of 500. Using mode 2, your percentage is (437 / 500) × 100 = 87.4%. For an aggregate across, say, five papers each out of 100, add every mark you obtained and divide by 500, then multiply by 100. To go the other way and convert a CGPA to a percentage, most Indian universities multiply CGPA by 9.5 — for that, use the dedicated CGPA to percentage calculator.

Worked example — a salary hike

If your salary rises from ₹50,000 to ₹60,000 a month, switch to mode 3 (percentage change): ((60,000 − 50,000) / 50,000) × 100 = 20%. The same formula tells you a stock that slips from ₹80 to ₹60 has changed by ((60 − 80) / 80) × 100 = −25% — the minus sign means a 25% fall.

GST and working backwards

To add 18% GST to a ₹1,000 base price: (18 / 100) × 1,000 = ₹180, total ₹1,180. To remove GST from a ₹1,180 inclusive price, divide by 1.18 to recover the ₹1,000 base — not 18% of ₹1,180, which is a common slip. The same reverse logic undoes a markup or a discount: divide by (1 + markup) to find the pre-markup price, or by (1 − discount) to find the pre-sale price. For a full bill with the CGST/SGST split, use our GST calculator, and for the discount-and-final-price flow see the discount calculator.

Quick mental-maths tricks

10% of any number = move the decimal one place left (10% of ₹4,500 = ₹450). 5% = half of 10%. 1% = move the decimal two places. To find 15%, add 10% + 5%. And a useful identity: X% of Y always equals Y% of X — so 18% of 50 is the same as 50% of 18 = 9, and the awkward-looking 4% of 75 is just 75% of 4 = 3, which you can do in your head.

Common mistakes to avoid

• Stacking discounts by adding them. “20% off, then an extra 10%” is not 30% off. The second cut applies to the already-reduced price: ₹1,000 → ₹800 → ₹720, an effective 28% off.
• Confusing percentage points with percent. An interest rate moving from 6% to 9% is a rise of 3 percentage points, but a 50% increase in the rate.
• Reversing a percentage by subtracting it back. A 20% rise followed by a 20% fall does not return to the start: ₹100 → ₹120 → ₹96.
• Removing GST as a flat percentage of the inclusive price. Divide by (1 + rate) instead, as shown above.