How to Calculate Percentage

Percentage is a way of expressing a number as a part of 100. The word 'percentage' comes from the Latin 'per centum', which means 'per hundred'. It is written using the symbol %.

For example, 75% means 75 out of every 100. If 75 students out of 100 passed an exam, we say the pass percentage is 75%.

Percentages are used everywhere — in school marks, shopping discounts, bank interest rates, GST, profit and loss, and even in health reports like body fat percentage.

The standard formula to calculate percentage is:

Percentage (%) = (Part ÷ Whole) × 100

Here, 'Part' is the value you want to find the percentage of, and 'Whole' is the total or reference value.

Example: If you scored 40 out of 50 in a test — Percentage = (40 ÷ 50) × 100 = 80%.

Step 1: Identify the Part and the Whole. The 'Part' is the smaller value. The 'Whole' is the total value.

Step 2: Divide the Part by the Whole. This gives a decimal number.

Step 3: Multiply the decimal by 100. The result is the percentage.

Example: A student scores 450 marks out of 500. Percentage = (450 ÷ 500) × 100 = 90%. The student scored 90%.

Another Example: A shop sold 80 items out of 200 in stock. Percentage sold = (80 ÷ 200) × 100 = 40%.

To calculate your percentage of marks, divide total marks obtained by maximum marks, then multiply by 100.

Formula: Marks Percentage = (Marks Obtained ÷ Total Marks) × 100

Example 1: Rahul scored 360 out of 400 in his Class 10 exams. Percentage = (360 ÷ 400) × 100 = 90%.

Example 2: Priya scored 525 out of 600 in Class 12 boards. Percentage = (525 ÷ 600) × 100 = 87.5%.

Tip: Many boards require a minimum of 33% or 35% to pass. Always check the passing criteria for your exam.

Sometimes you need to find X% of a given number. The formula is:

Value = (Percentage ÷ 100) × Number

Example 1: What is 20% of 500? Value = (20 ÷ 100) × 500 = 100.

Example 2: What is 15% of ₹2,000? Value = (15 ÷ 100) × 2000 = ₹300.

This is commonly used to calculate discounts, GST amounts, and commission.

Percentage increase tells you by how much percent a value has gone up compared to the original value.

Formula: Percentage Increase = ((New Value − Original Value) ÷ Original Value) × 100

Example 1: A salary increased from ₹20,000 to ₹25,000. Increase = ((25000 − 20000) ÷ 20000) × 100 = 25%. The salary increased by 25%.

Example 2: A product's price went from ₹100 to ₹120. Increase = ((120 − 100) ÷ 100) × 100 = 20%.

Use this formula to track price hikes, population growth, revenue growth, or salary appraisals.

Percentage decrease tells you by how much percent a value has gone down compared to the original value.

Formula: Percentage Decrease = ((Original Value − New Value) ÷ Original Value) × 100

Example 1: A product was priced at ₹1,000 and is now sold for ₹800. Decrease = ((1000 − 800) ÷ 1000) × 100 = 20%.

Example 2: A company's sales dropped from 5,000 units to 3,500 units. Decrease = ((5000 − 3500) ÷ 5000) × 100 = 30%.

This formula is useful in tracking price drops, sales decline, weight loss, or stock market falls.

When a product is on sale, the discount is usually expressed as a percentage of the original price.

Formula: Discount Amount = (Discount % ÷ 100) × Original Price

Sale Price = Original Price − Discount Amount

Example: A shirt costs ₹800 and has a 25% discount. Discount = (25 ÷ 100) × 800 = ₹200. Sale Price = 800 − 200 = ₹600.

You can also work backwards — if the sale price and discount percentage are known, the original price = Sale Price ÷ (1 − Discount%/100).

In business and commerce, profit and loss are always expressed as a percentage of the cost price.

Profit % = ((Selling Price − Cost Price) ÷ Cost Price) × 100

Loss % = ((Cost Price − Selling Price) ÷ Cost Price) × 100

Example 1: A shopkeeper buys an item for ₹500 and sells it for ₹600. Profit = ₹100. Profit % = (100 ÷ 500) × 100 = 20%.

Example 2: A phone bought for ₹15,000 is sold for ₹12,000. Loss = ₹3,000. Loss % = (3000 ÷ 15000) × 100 = 20%.

GST (Goods and Services Tax) in India is applied as a percentage on the base price of goods and services.

Formula: GST Amount = (GST Rate ÷ 100) × Base Price

Total Price = Base Price + GST Amount

Example: A product costs ₹1,000 and has 18% GST. GST = (18 ÷ 100) × 1000 = ₹180. Total price = ₹1,000 + ₹180 = ₹1,180.

Common GST slabs in India are 5%, 12%, 18%, and 28% depending on the type of product or service.

Trick 1 — 10% of any number: Simply move the decimal one place to the left. 10% of 450 = 45.

Trick 2 — 5% of any number: Find 10% first, then halve it. 5% of 450 = 45 ÷ 2 = 22.5.

Trick 3 — 25% of any number: Divide the number by 4. 25% of 800 = 800 ÷ 4 = 200.

Trick 4 — 50% of any number: Divide the number by 2. 50% of 640 = 320.

Trick 5 — X% of Y = Y% of X: This is a useful swap trick. 8% of 25 = 25% of 8 = 2. Always pick the easier side to calculate.

School & College: Percentage of marks in exams, attendance percentage, and cut-off percentages for college admissions.

Shopping: Discount percentage on products during sales, cashback percentages on payment apps.

Finance & Banking: Interest rates on loans and FDs, EMI calculations, and return on investment (ROI).

Taxes: Income tax slabs, GST rates, TDS deductions — all expressed as percentages.

Health: Body fat percentage, blood sugar levels reported as percentage values, COVID recovery rates.

Business: Profit margin percentage, market share percentage, employee appraisal ratings.

Understanding percentages makes you better at managing money, evaluating offers, and making smarter decisions in daily life.