How to Calculate Percentages — Complete Guide
Percentages appear in everyday life — from GST on purchases to bank interest, exam marks, and sale discounts. Mastering a few simple formulas makes all percentage calculations easy.
1. Finding X% of a Number
Formula: (X ÷ 100) × Y
Example: What is 18% GST on ₹2,500?
(18 ÷ 100) × 2,500 = 0.18 × 2,500 = ₹450
2. What Percentage is X of Y?
Formula: (X ÷ Y) × 100
Example: You scored 450 out of 600. What percentage?
(450 ÷ 600) × 100 = 75%
3. Percentage Increase / Decrease
Formula: ((New − Old) ÷ Old) × 100
Example: Salary increased from ₹40,000 to ₹48,000.
((48,000 − 40,000) ÷ 40,000) × 100 = 20% increase
4. Adding GST to a Price
Formula: Price × (1 + GST%/100)
Example: ₹1,000 product with 18% GST:
1,000 × 1.18 = ₹1,180 total
5. Finding Base Price from GST-Inclusive Amount
Formula: Inclusive Price ÷ (1 + GST%/100)
Example: You paid ₹1,180 including 18% GST. Original price?
1,180 ÷ 1.18 = ₹1,000
Common Percentage Shortcuts
| To find | Shortcut |
|---|---|
| 10% of any number | Move decimal one place left |
| 5% of any number | Half of 10% |
| 25% of any number | Divide by 4 |
| 50% of any number | Divide by 2 |
| 1% of any number | Move decimal two places left |
🧮 Quick tip: To calculate any percentage quickly, break it up. 18% = 10% + 8% = 10% + (10%/2) + (10%/10×8). Or just use our percentage calculator above!