Discount Calculator Formulas
Sale Price (after discount)
Sale Price = Original Price × (1 − Discount% / 100)
Example: ₹2000 at 25% off = 2000 × 0.75 = ₹1500
Find % off (when you know both prices)
% off = ((Original − Sale) / Original) × 100
Example: Original ₹2000, sale ₹1400 → ((2000−1400)/2000) × 100 = 30% off
% of a number
X% of Y = (X / 100) × Y
Example: 20% of 500 = 0.20 × 500 = 100
Percentage change
% change = ((New − Old) / Old) × 100
If positive → increase. If negative → decrease.
When to Use Each Mode
- Discount Price — when shopping: "₹2000 with 25% off, how much do I pay?"
- What's % Off — comparing deals: "Was ₹2000, now ₹1500. What's the discount?"
- % of Number — general math: "What is 18% of ₹5000?" (e.g. tip, tax)
- % Change — comparing values over time: "My salary went from ₹50K to ₹65K, what's the raise %?"
Real-World Examples
Shopping
- Sale tag: "Flat 40% off" on ₹5000 t-shirt → You pay ₹3000, save ₹2000
- "₹1199 from ₹1999" → You're getting 40% off, saving ₹800
- "Buy 2, get 1 free" on ₹500 items → Effective 33.3% discount per piece
Salary / Career
- Old salary ₹50K, new ₹65K → 30% hike
- Asking for 25% hike on ₹40K → expect ₹50K offer
- Inflation 6%, salary hike 8% → real raise = ~2%
Finance & Tax
- 18% GST on ₹1000 = ₹180 added → total ₹1180
- 10% TDS on ₹50K rent = ₹5000 deducted
- Investment grew from ₹1L to ₹1.5L → 50% return
Frequently Asked Questions
How do you calculate the discount price?
Discount amount = Original price × (Discount % / 100). Sale price = Original − Discount amount. Example: ₹1000 at 20% off = ₹1000 × 0.20 = ₹200 discount, sale price = ₹800.
How to find the percentage off when both prices are known?
% off = ((Original − Sale) / Original) × 100. Example: Original ₹1000, sale ₹750 → ((1000−750)/1000) × 100 = 25% off.
What's the difference between % off and % markup?
% off is based on Original price (going down). % markup is based on Cost price (going up). A 50% markup on ₹100 = ₹150 sale. A 50% off from ₹100 = ₹50 sale.
How to calculate compound discounts (e.g., 20% off then extra 10%)?
Apply sequentially, not additively. ₹1000 with 20% off = ₹800. Then 10% off ₹800 = ₹720. Total effective discount = 28%, not 30%.
What if I want to know the original price from the sale price?
Use this formula: Original = Sale ÷ (1 − Discount% / 100). Example: Sale ₹750 with 25% off → Original = 750 / 0.75 = ₹1000.
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