Percentage Calculation Guide: Formulas, Tricks, and Real-Life Examples
Percentage is used everywhere: marks, discounts, salary hikes, GST bills, and investment returns. This guide gives quick formulas and practical examples you can apply instantly.
1. Core Percentage Formula
The most important formula is:
Percentage = (Part / Whole) × 100
Example: You scored 72 out of 90 in a test.
- Part = 72
- Whole = 90
- Percentage = (72 / 90) × 100 = 80%
2. How to Find X% of a Number
Use this formula:
X% of N = (X / 100) × N
Examples:
- 15% of 2,000 = 0.15 × 2,000 = 300
- 8% of 7,500 = 0.08 × 7,500 = 600
- 2.5% of 40,000 = 0.025 × 40,000 = 1,000
3. Percentage Increase Formula
Use percentage increase when price, salary, or quantity goes up:
% Increase = ((New − Old) / Old) × 100
Example: Salary increases from ₹40,000 to ₹46,000.
- Increase = 46,000 − 40,000 = 6,000
- % Increase = (6,000 / 40,000) × 100 = 15%
4. Percentage Decrease Formula
Use percentage decrease when value drops:
% Decrease = ((Old − New) / Old) × 100
Example: Mobile price drops from ₹25,000 to ₹20,000.
- Decrease = 5,000
- % Decrease = (5,000 / 25,000) × 100 = 20%
5. Discount Percentage and Final Price
For shopping and sales, two formulas are useful:
- Discount Amount = (Discount% / 100) × Marked Price
- Final Price = Marked Price − Discount Amount
Example: 30% off on ₹3,500:
- Discount = 0.30 × 3,500 = ₹1,050
- Final Price = 3,500 − 1,050 = ₹2,450
6. Reverse Percentage (Find Original Value)
Sometimes you know the result after increase/decrease and need original value.
Original = Final / (1 ± Rate)
Use + for increase and - for decrease.
- If ₹1,600 is after 20% discount: Original = 1,600 / 0.8 = ₹2,000
- If ₹11,500 is after 15% hike: Original = 11,500 / 1.15 = ₹10,000
7. Marks, GST, and Profit Margin Examples
Marks Percentage
If marks are 438 out of 500, percentage = (438/500)×100 = 87.6%.
GST Add-on
If product price is ₹2,000 and GST is 18%, GST = ₹360, final bill = ₹2,360.
Profit Percentage
If cost price is ₹800 and selling price is ₹1,000, profit = ₹200. Profit% = (200/800)×100 = 25%.
8. Common Percentage Mistakes to Avoid
- Using wrong base value (always divide by original/base value)
- Adding percentage points and percentages as if they are same
- Applying increase and decrease on the wrong amount
- Forgetting that 20% increase followed by 20% decrease does not return to original value
- Rounding too early in multi-step calculations
Quick Reference Table
| Use Case | Formula |
|---|---|
| Part as % of Whole | (Part / Whole) × 100 |
| X% of N | (X / 100) × N |
| % Increase | ((New − Old) / Old) × 100 |
| % Decrease | ((Old − New) / Old) × 100 |
| Original from final (reverse %) | Final / (1 ± Rate) |
Frequently Asked Questions
How do I calculate percentage of a number?
Use (Part ÷ Whole) × 100. Example: 18 out of 60 is (18/60)×100 = 30%.
How to calculate percentage increase?
Use ((New Value − Old Value) ÷ Old Value) × 100. Example: 500 to 650 is ((650−500)/500)×100 = 30% increase.
What is percentage decrease formula?
Use ((Old Value − New Value) ÷ Old Value) × 100. Example: 900 to 720 is ((900−720)/900)×100 = 20% decrease.
How do I find original price after discount?
If discounted price is known, divide by (1 − discount%). Example: ₹1,600 after 20% discount means original = 1600/0.8 = ₹2,000.
Which calculator should I use for percentages and discounts?
Use CalcVerse Percentage Calculator for direct percentage problems and Discount Calculator for shopping discount and savings calculations.
Practice with Free Tools
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