Three Percentage Problems, One Calculator
“Per cent” simply means “out of 100”. Percentages show up everywhere — exam marks, salary hikes, GST, discounts, interest rates, election results and business growth. Almost every everyday percentage question is one of three types, and this calculator has a mode for each:
| Mode | Question it answers | Example |
|---|---|---|
| X% of Y | What is a given percentage of a number? | What is 18% of ₹2,500? |
| X is % of Y | What percentage is one number of another? | 45 is what % of 60? |
| % Increase / Decrease | By what percentage did a value change? | Price went from ₹80 to ₹100 |
How to Use the Percentage Calculator
- Choose the mode that matches your question.
- Enter the two values. The helper text under the boxes shows the question in plain words, so you can check you have put the numbers the right way round.
- The answer appears instantly, along with a short explanation.
Percentage Formulas with Examples
1. Finding X% of Y
Example: 18% GST on ₹2,500 = 2,500 × 18 ÷ 100 = ₹450.
Mental shortcut: 10% of any number is that number divided by 10. So 10% of 2,500 is 250, 5% is half of that (125), and 15% is 250 + 125 = 375.
2. Finding what percent X is of Y
Example: You scored 450 out of 600 in your exams: 450 ÷ 600 × 100 = 75%.
3. Percentage increase or decrease
Example: Your salary goes from ₹40,000 to ₹46,000: (46,000 − 40,000) ÷ 40,000 × 100 = 15% increase. If petrol drops from ₹105 to ₹100, the change is (100 − 105) ÷ 105 × 100 = −4.76%, a decrease.
Common Percentage Mistakes
Percentage changes are not symmetric
If a share price falls 20% from ₹100 to ₹80, a 20% rise only takes it to ₹96. It needs a 25% rise to return to ₹100. The bigger the fall, the larger the recovery needed: a 50% loss needs a 100% gain to break even.
Percent vs percentage points
When a home loan rate moves from 8% to 9%, it has risen by 1 percentage point, but the rate itself is 12.5% higher. News reports sometimes mix these up, so it is worth knowing the difference.
Using the wrong base
The “old” value is always the base for percentage change. Going from 50 to 75 is a 50% increase, but going from 75 back to 50 is a 33.3% decrease.
Everyday Uses
- Students: marks percentage, attendance percentage, and checking answers in maths and commerce.
- Shopping: discount and GST calculations.
- Work and business: salary hikes, sales growth, profit margins and targets.
- Personal finance: how much of your income goes to rent, EMIs or savings.
Related Tools
- Discount Calculator — sale price and savings with optional tax.
- GST Calculator — add or remove GST at any slab.
- SIP Calculator — see how a percentage return compounds over time.