Percentage Calculator — How to Calculate Percentages Online

Percentages are everywhere — from a 30% discount at your favourite store to the 18% GST on your restaurant bill, from your exam score to your salary hike letter. Yet many people still reach for a calculator and wonder, "Am I doing this right?" This guide explains exactly how to calculate percentages using clear formulas and everyday examples, so you never get confused again.

Whether you are a student solving math problems, a shopper comparing deals, a business owner computing tax, or an employee evaluating a pay rise, mastering percentage calculations is one of the most practical math skills you can have. And if mental math is not your strong suit, our free percentage calculator does the heavy lifting in a single click.

What Is a Percentage?

A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin per centum, meaning "per hundred." When you say 45%, you mean 45 out of every 100 — or 45/100 = 0.45 in decimal form.

Percentages make comparisons easy. If one student scores 68/80 and another scores 51/60, it is hard to compare directly. Convert both to percentages — 85% vs 85% — and the comparison is instant. That is why percentages are used universally in finance, science, statistics, health, and daily life.

Three core elements are always involved in a percentage problem: the base (the whole), the part (the portion), and the percentage (the rate). Knowing any two of these lets you find the third — which is exactly what the four calculation types below cover.

4 Types of Percentage Calculations

Almost every percentage problem you will ever encounter falls into one of four types. Recognising which type you are dealing with is the first step to solving it correctly.

#	Question Type	Example	Answer
1	What is X% of Y?	What is 20% of 500?	100
2	X is what % of Y?	40 is what % of 200?	20%
3	X is Y% of what?	60 is 30% of what?	200
4	% change (increase/decrease)	From 400 to 500?	+25%

Each type has its own formula. Once you have the right formula, the arithmetic is straightforward — or you can just punch the numbers into our percentage calculator and get the answer instantly.

Percentage Formulas Explained

Let us break down each formula clearly so you understand what is happening mathematically.

Type 1 — Finding the Part: What is X% of Y?

Formula: Part = (X / 100) × Y

Example: What is 15% of 800?
Part = (15 / 100) × 800 = 0.15 × 800 = 120

Type 2 — Finding the Rate: X is what % of Y?

Formula: Percentage = (X / Y) × 100

Example: 75 is what % of 300?
Percentage = (75 / 300) × 100 = 0.25 × 100 = 25%

Type 3 — Finding the Base: X is Y% of what?

Formula: Base = X / (Y / 100) = (X × 100) / Y

Example: 90 is 45% of what?
Base = (90 × 100) / 45 = 9000 / 45 = 200

Type 4 — Percentage Change

Formula: % Change = ((New Value − Old Value) / Old Value) × 100

A positive result is an increase; a negative result is a decrease.
Example: Price rose from ₹600 to ₹750.
% Change = ((750 − 600) / 600) × 100 = (150 / 600) × 100 = +25%

Real-World Examples

Understanding formulas is one thing; seeing them applied to real situations is where it all clicks. Below are four common scenarios where percentage calculations come up in everyday life.

These examples are designed to walk you through the logic step by step, so you can apply the same reasoning to any situation you face — whether it is calculating a tip at a restaurant, understanding your tax invoice, or comparing investment returns.

Shopping & Discounts

Shopping discounts are probably the most common place most people use percentages. You see "30% Off" on a ₹2,499 jacket. How much do you actually pay?

Step 1: Find the discount amount.
Discount = (30 / 100) × 2499 = ₹749.70

Step 2: Subtract from original price.
Final Price = 2499 − 749.70 = ₹1,749.30

What if two stores offer different deals — Store A gives 25% off ₹1,200 and Store B gives 30% off ₹1,400? Calculate both final prices: Store A = ₹900, Store B = ₹980. Store A is cheaper despite the lower discount percentage. This is why knowing how to calculate percentages saves you real money. Use the discount calculator for quick comparisons.

Exam Scores & Grades

Students constantly convert marks to percentages. If you scored 342 out of 400 in your board exam, what is your percentage?

Percentage = (342 / 400) × 100 = 85.5%

Many universities use grade boundaries based on percentage ranges. Knowing your exact percentage helps you understand which grade band you fall into — whether that is Distinction (75%+), First Class (60–75%), or Second Class (50–60%). It is also useful for calculating how much you need to score in remaining papers to achieve a target percentage for the year.

For a weighted GPA system, each subject may carry a different credit weight. In that case, multiply each subject's percentage by its credit weight, sum all the weighted scores, and divide by the total credits — a weighted average that requires the same percentage logic.

Salary Hikes & GST

When your employer offers a 12% salary hike on a CTC of ₹6,50,000, your new CTC is:

Hike Amount = (12 / 100) × 650000 = ₹78,000
New CTC = 650000 + 78000 = ₹7,28,000

GST works on the same principle. If a product costs ₹1,000 and attracts 18% GST (the most common slab), the GST amount is ₹180 and the final price is ₹1,180. For reverse GST — extracting the tax from an inclusive price — the formula changes: GST Amount = (Price × Rate) / (100 + Rate). So if a bill is ₹1,180 inclusive of 18% GST, the base price is (1180 × 100) / 118 = ₹1,000. Try our GST calculator for instant inclusive/exclusive calculations.

Common Percentage Mistakes

Even people who understand percentages make these errors regularly. Knowing them helps you avoid costly mistakes.

• Adding percentages directly: A 20% increase followed by a 20% decrease does NOT return to the original value. 100 → +20% → 120 → −20% → 96. You are down 4%.
• Wrong base: "50% more than X" and "50% of X" are very different. Always confirm what the base is.
• Confusing percentage points with percentages: If inflation rises from 4% to 6%, it rose by 2 percentage points — but by 50% in percentage terms.
• Rounding too early: If you round intermediate steps, the final answer accumulates rounding error. Keep full precision until the final result.
• Percentage of a percentage: "10% of 20%" is not 30% — it is 0.10 × 0.20 = 0.02, or 2%.

Tips for Quick Mental Calculation

You do not always have a calculator handy. These mental shortcuts let you estimate percentages quickly:

• 10% trick: Move the decimal one place left. 10% of ₹850 = ₹85.
• 5% = half of 10%: 5% of ₹850 = ₹42.50.
• 20% = double 10%: 20% of ₹850 = ₹170.
• 25% = divide by 4: 25% of ₹800 = ₹200.
• 1% base: Find 1% first (divide by 100), then multiply. 7% of ₹430: 1% = ₹4.30, × 7 = ₹30.10.
• Reverse trick: X% of Y = Y% of X. So 8% of 25 = 25% of 8 = 2. Often easier!

For anything more complex, our online percentage calculator handles all four calculation types — just enter two values and it returns the third with a step-by-step explanation.

Frequently Asked Questions