Discount Calculator

Sale season math, solved: final price, your savings, stacked "extra %" offers and tax — instantly.

The discount formula

Final price = original price × (100 − discount) ÷ 100. A 30% discount means you pay 70% of the price: an item at 2,400 costs 2,400 × 0.70 = 1,680, saving you 720.

Stacked discounts don't add up. "30% off + extra 10%" is not 40% off — the extra 10% applies to the already-reduced price: 2,400 → 1,680 → 1,512. That's a true total discount of 37%, not 40%. Stores rely on shoppers not noticing the difference; this calculator shows the real combined percentage.

Smart shopping checks

• Compare final prices, not discount percentages. 40% off an inflated price can cost more than 20% off an honest one.
• Watch the base price before sales. Some retailers raise prices shortly before "50% off" events.
• Per-unit price wins. For groceries, divide final price by weight/quantity to compare pack sizes fairly.

How stacked discounts really work

Extra discounts multiply, they don't add. "30% off plus an extra 10%" applies the 10% to the already-reduced price, giving a true discount of 37%, not 40%. The calculator shows the real combined percentage so you can compare offers honestly and spot when a big-sounding stacked deal is smaller than it looks.

Finding the original price from a sale price

Sometimes you know the sale price and the discount, and want the original. If an item is 30% off and costs 1,680, it represents 70% of the original, so divide: 1,680 ÷ 0.70 = 2,400. This helps you check whether an advertised "was" price is genuine.

Which is the better deal: % off, or "buy one get one"?

Shops present offers in ways that are hard to compare on the spot, so convert everything to a price per unit and the winner becomes obvious.

Take an item at 500. A straight 30% off gives you one unit for 350. Buy one get one free gives two units for 500, so 250 each — better, but only if you actually want two. Buy two get one free gives three for 1,000, or 333 each. Buy one get one half price gives two for 750, or 375 each — the weakest of the four, despite sounding generous. Ranked by unit price: BOGOF, then 3-for-2, then 30% off, then BOGO-half-price.

The catch is that multi-buy offers only save money on things you would have bought anyway. Two of something you didn't need at 250 each is 500 spent, not 500 saved.

Why 50% off then 20% off is not 70% off

Stacked discounts apply one after another, each to the already reduced price — so they never add up the way the signage implies. On a 1,000 item: 50% off brings it to 500, then 20% off that takes 100 more, landing at 400. That is a 60% total reduction, not 70%.

The shortcut is to multiply what remains rather than adding what comes off: 0.50 × 0.80 = 0.40, so you pay 40% of the original. Useful consequence — the order never matters. Applying 20% then 50% gives exactly the same 400, so don't let a cashier tell you the sequence matters.

The reference price trap

A percentage is only meaningful relative to an honest starting price, and that is where most "deals" fall down. Watch for prices raised shortly before a sale so the discount looks bigger, "RRP" or "was" figures the item never actually sold at, and permanent sales where the discounted price is simply the real price.

The defence is simple: ignore the percentage and judge the final price. Ask what the item is worth to you, and check one or two other sellers. A genuine 20% off a fair price beats a theatrical 70% off an invented one.

Frequently asked questions