How to Calculate Percentage: Every Formula You'll Ever Need

Calculate percentages instantly

The 3 basic percentage formulas

Every percentage calculation in existence is a variation of three fundamental formulas. Master these three and you can solve anything.

Formula 1: Find the percentage (what % is X of Y?)

Example: You scored 420 out of 500. What's your percentage?
(420 ÷ 500) × 100 = 84%

Formula 2: Find the part (what is X% of Y?)

Example: What is 18% of ₹12,500? (GST calculation)
(18 × 12,500) ÷ 100 = ₹2,250

Formula 3: Find the whole (X is Y% of what?)

Example: ₹3,600 is 12% of the total bill. What's the total?
(3,600 × 100) ÷ 12 = ₹30,000

These three formulas are the same equation rearranged. If you know any two of the three values (part, whole, percentage), you can always find the third. Our Percentage Calculator solves all three variations.

How to find percentage of a number

This is the most common percentage calculation — "What is X% of Y?"

The formula

Worked examples

The shortcut: Convert the percentage to a decimal by dividing by 100 (or moving the decimal point two places left), then multiply. 25% = 0.25. 18% = 0.18. 8.5% = 0.085. This eliminates the "÷ 100" step and makes mental math easier.

What percentage is X of Y?

"I scored 380 out of 500 — what's my percentage?" This flips the first formula.

The formula

Worked examples

Yes, percentages can exceed 100%. "Sales are 150% of target" means sales are 1.5× the target. Our Percentage Calculator handles all ranges.

How to calculate percentage increase

Used for: salary hikes, price increases, population growth, investment returns, inflation rates.

The formula

Worked examples

Key: Always divide by the OLD value, not the new one. This is the most common mistake in percentage increase calculations. Our Percentage Calculator handles this automatically.

Tracking your salary hike percentage? See how it affects your take-home with our Salary Calculator. Planning investments based on expected returns? Use our SIP Calculator.

How to calculate percentage decrease

Same formula as increase, but the result is negative (or you take the absolute value and call it a "decrease").

The formula

Worked examples

Important asymmetry: A 50% decrease followed by a 50% increase does NOT return to the original. ₹100 → 50% decrease → ₹50 → 50% increase → ₹75. You need a 100% increase to recover from a 50% decrease. This is why stock market crashes hurt more than equivalent rallies help.

Percentage difference between two numbers

When there's no clear "old" and "new" — just two values you're comparing — use percentage difference.

The formula

The denominator uses the average of both values, making the comparison symmetric — the result is the same regardless of which number you call Value1 or Value2.

Example

Company A has 450 employees. Company B has 380 employees. What's the percentage difference?

• Difference: |450 - 380| = 70
• Average: (450 + 380) ÷ 2 = 415
• % Difference: (70 ÷ 415) × 100 = 16.9%

When to use difference vs increase/decrease

• Percentage increase/decrease: When one value is clearly the "before" and the other is "after" (salary before and after hike, price before and after discount)
• Percentage difference: When comparing two independent values with no time relationship (two companies, two products, two cities)

How to calculate marks percentage (exams)

This is the percentage calculation that every Indian student needs multiple times a year — board exams, entrance tests, semester results, competitive exams.

Single subject

Example: Scored 78 out of 100 in Mathematics.
(78 ÷ 100) × 100 = 78%

Multiple subjects (aggregate percentage)

Worked example: CBSE Board Results

Aggregate percentage = (415 ÷ 500) × 100 = 83%

When subjects have different total marks

Some exams have subjects with different totals (e.g., one subject out of 50, another out of 100). The formula still works — just add all obtained marks and divide by all total marks.

Example: Physics 42/50, Chemistry 38/50, Biology 72/100.
Total obtained: 42 + 38 + 72 = 152
Total possible: 50 + 50 + 100 = 200
Percentage: (152 ÷ 200) × 100 = 76%

Need to convert your percentage to GPA? Use our GPA Calculator.

How to calculate discount percentage

Essential for shopping — every Amazon sale, Flipkart Big Billion Days, and local store promotion uses percentage discounts.

Finding the discount percentage

Example: Shirt was ₹1,499, now ₹1,049.
((1,499 - 1,049) ÷ 1,499) × 100 = (450 ÷ 1,499) × 100 = 30% off

Finding the sale price from a discount

Example: ₹2,000 item with 35% discount.
₹2,000 × (1 - 0.35) = ₹2,000 × 0.65 = ₹1,300

Stacked discounts (additional % off)

"40% off + additional 20% off" does NOT equal 60% off. The second discount applies to the already-discounted price:

• ₹1,000 item, 40% off = ₹600
• Additional 20% off ₹600 = ₹480
• Total effective discount = 52%, not 60%

Formula for stacked discounts:
Effective discount = 1 - ((1 - D1/100) × (1 - D2/100))
= 1 - (0.60 × 0.80) = 1 - 0.48 = 0.52 = 52%

Use our Discount Calculator to quickly find the final price after any single or stacked discount.

How to calculate GST percentage

GST is the most common tax percentage calculation in India. Here are the essential formulas:

Adding GST to a price

Example: ₹5,000 item with 18% GST.
₹5,000 × (1 + 0.18) = ₹5,000 × 1.18 = ₹5,900

Finding the base price from a GST-inclusive price

Example: Bill shows ₹11,800 (18% GST inclusive). What's the base price?
₹11,800 ÷ 1.18 = ₹10,000
GST amount = ₹11,800 - ₹10,000 = ₹1,800

Common Indian GST rates

Use our GST Calculator for instant calculations — enter the base price and GST rate, see the GST amount and total price.

How to calculate salary hike percentage

Appraisal season in India (April-June) means everyone's calculating their salary hike. Here's how:

The formula

Worked examples

Hike on CTC vs hike on in-hand

Critical distinction: A 15% hike on CTC does NOT mean 15% more in your bank account. Higher CTC means higher PF contribution and potentially higher tax bracket. A 15% CTC hike might translate to only 10-12% increase in in-hand salary.

Calculate the actual in-hand impact with our Salary Calculator. Enter both your old and new CTC to see the real difference in monthly take-home. Read our detailed guide: CTC vs In-Hand Salary Explained.

Mental math shortcuts for percentages

You don't always need a calculator. These tricks let you estimate percentages in your head:

The anchor method

Start with easy percentages and work from there:

• 10% of anything: Move the decimal one place left. 10% of 8,500 = 850
• 5% of anything: Half of 10%. 5% of 8,500 = 425
• 1% of anything: Move the decimal two places left. 1% of 8,500 = 85
• 25% of anything: Divide by 4. 25% of 8,500 = 2,125
• 50% of anything: Divide by 2. 50% of 8,500 = 4,250
• 20% of anything: Divide by 5. 20% of 8,500 = 1,700

Building complex percentages from simple ones

15% = 10% + 5%: 15% of 8,500 = 850 + 425 = 1,275
12% = 10% + 1% + 1%: 12% of 8,500 = 850 + 85 + 85 = 1,020
18% = 20% - 2%: 18% of 5,000 = 1,000 - 100 = 900
30% = 3 × 10%: 30% of 8,500 = 3 × 850 = 2,550
75% = 50% + 25%: 75% of 8,500 = 4,250 + 2,125 = 6,375

The reverse trick

X% of Y = Y% of X. Always.

Example: 8% of 50 is hard to calculate mentally. But 50% of 8 = 4. Same answer! So 8% of 50 = 4.

This works because (8/100 × 50) = (50/100 × 8). Use whichever direction is easier to compute.

The "double and halve" trick for shopping discounts

30% off ₹1,200: Hard.
30% off ₹1,000 = ₹300. 30% off ₹200 = ₹60. Total: ₹360 off.
Sale price: ₹1,200 - ₹360 = ₹840.

Break numbers into round components for easier mental math. Our Discount Calculator does the hard work for complex discounts.

Frequently Asked Questions