How to Calculate Discounts Quickly
Whether you're shopping sales, calculating trade discounts for business, or figuring out tip-plus-discount scenarios, understanding discount math saves you money and prevents you from being misled by misleading "sale" pricing.
Quick Mental Math for Common Discounts
- 10% off — Move the decimal one place left. $85 → $8.50 off → $76.50
- 20% off — Find 10%, double it. $85 → $8.50 × 2 = $17 off → $68
- 25% off — Divide by 4. $80 → $20 off → $60
- 50% off — Divide by 2. $85 → $42.50
- 15% off — Find 10% + half of 10%. $80 → $8 + $4 = $12 off → $68
Frequently Asked Questions
How do I calculate a percentage off a price?
Multiply the original price by (1 - discount rate). For 30% off a $120 item: $120 × (1 - 0.30) = $120 × 0.70 = $84. Or: find 30% of $120 ($36) and subtract it from $120 = $84.
How do stacked discounts work?
Stacked discounts (e.g., 20% off then an extra 10% off) don't add up to 30%. You apply them sequentially: $100 → 20% off = $80 → 10% off $80 = $72. The combined discount is 28%, not 30%. Retailers use this to make discounts sound larger than they are.