How to Calculate Discounts — and See Through Sale Tricks
Sale season rewards the shopper who can do the math. Here's the 5-second method, plus the pricing games stores hope you won't notice.
The 5-second method
Don't compute the discount and subtract — compute what you pay. 30% off means you pay 70%: price × 0.70, one step. An item at 2,400 → 2,400 × 0.7 = 1,680. For mental math, anchor on 10%: 10% of 2,400 is 240, so 30% is 720, pay 1,680. Same answer, no calculator.
Why "30% + extra 10%" is not 40%
Stacked discounts multiply, they don't add. The extra 10% applies to the already reduced price: 2,400 → 1,680 → 1,512. That's a true discount of 37%, not 40%. The difference looks small on one item and becomes real money on a big cart — and it's precisely why stores advertise stacked offers instead of a single honest percentage.
Four pricing tricks to watch for
- The inflated "original" price. The tag says 50% off 4,000 — but the item sold at 2,400 last month. Judge the final price, not the percentage.
- Charm pricing: 1,999 reads as "one thousand something." Round it up in your head before deciding.
- "Up to 70% off": the "up to" items are usually a handful of leftovers; the rack average is far lower.
- Shrinking pack sizes: the price stays, the grams drop. Compare per-unit price (price ÷ weight), not pack price.
Tax after discount
In most places sales tax or VAT is charged on the discounted price: a 1,512 item with 5% tax rings up at 1,587.60. If a store charges tax on the pre-discount price, that's worth questioning at the counter.
Frequently asked questions
How do I calculate 30% off a price?
Multiply by 0.70 — you pay 70%. 2,400 becomes 1,680.
Is 30% off plus an extra 10% the same as 40% off?
No — the extra 10% applies to the reduced price. True total: 37% off.
How can I tell if a sale is genuine?
Compare the final price across stores and against the item's usual price — not against the printed "original" price.