Discount Calculator
Discount rate and sale price.
Sale price
0원
Discount rate
0%
What is discount calculation?
Computes the actual sale price after applying a discount rate to the original price, and the amount saved. It can also work in reverse, deriving the discount rate from the original and sale prices.
How to use it
On the “Sale price” tab, enter the original price and discount rate (%) to see the sale price and savings. On the “Reverse rate” tab, enter the original and sale price to reverse-calculate the discount rate.
Formulas
Sale price = Original × (1 − rate ÷ 100)
Saved = Original − Sale price
Rate (%) = (1 − Sale price ÷ Original) × 100
The double-discount trap — 10% + 10% is 19%, not 20%
When two discounts stack — say, 10% off, then another 10% off — it's tempting to assume a combined 20% discount, but the real total is smaller. A 10,000 KRW item discounted 10% becomes 9,000 KRW, and applying another 10% to that 9,000 KRW gives 9,000 × 0.9 = 8,100 KRW.
Comparing the original 10,000 KRW to the final 8,100 KRW gives a total discount of (10,000−8,100) ÷ 10,000 × 100 = 19% — less than the naive sum of 20%. That's because the second discount applies to an already-reduced amount, not the original price. When discounts stack, running this calculator's "Sale price" tab twice in sequence gives the accurate final price.
"N% off now" vs. "N% cashback points" — which is the better deal?
"5% off right now" and "5% back in points" look identical as numbers, but the real benefit differs. On a 10,000 KRW item, a 5% instant discount means paying just 9,500 KRW on the spot, while 5% in points means paying the full 10,000 KRW at checkout and getting 500 KRW worth of points back later.
Points often come with expiration dates or minimum-use conditions, so if you never fully redeem them, the real benefit ends up below 5%. An instant discount, by contrast, is a guaranteed reduction at the moment of purchase — so for the same headline number, an instant discount is generally the safer value.
Comparing unit prices — look past the discount rate to price per gram or ml
When comparing two products in different package sizes, the discount rate alone can mislead — unit price (per gram, per ml, per item) tells you which one is actually cheaper. For example, Product A (500g, 8,000 KRW) discounted 20% comes to 6,400 KRW, or 12.8 KRW per gram, while Product B (1kg, 11,000 KRW) discounted 10% comes to 9,900 KRW, or 9.9 KRW per gram.
Looking only at the discount rate, A (20%) seems like the better deal over B (10%) — but B actually has the lower price per gram. Checking the unit price often shown on supermarket shelf tags, or simply dividing the sale price by quantity yourself, keeps you from being fooled by the discount-rate illusion.