Discount Calculator
Find the sale price and what you actually save — including stacked coupons.
You pay
80.00
You save
20.00
Total discount
20.0%
Find the sale price after a percentage discount, or work out how much you actually saved, including stacking multiple sequential discounts or coupons — which is not the same as adding the percentages together.
This matters because a 20% discount followed by a 10% coupon isn't a flat 30% off; each discount applies to the already-reduced price, so the effective total discount is smaller than a simple sum.
What stacked discounts really come to
| Advertised | You actually pay | True total discount |
|---|---|---|
| 20% off, then 10% off | 72% of list | 28%, not 30% |
| 30% off, then 20% off | 56% of list | 44%, not 50% |
| 50% off, then 50% off | 25% of list | 75%, not 100% |
| 10% off three times | 72.9% of list | 27.1%, not 30% |
Stacked percentages multiply rather than add. The order doesn't matter for two percentage discounts — but it matters enormously when a flat-amount coupon is involved.
Order matters when a flat coupon is in the mix
On a $100 item with a 20% discount and a $15 coupon, taking the percentage first leaves you paying $65. Applying the coupon first leaves you paying $68. The difference is $3, and which order applies is decided by the retailer's checkout, not by you.
As a rule you want percentage discounts applied to the largest possible base, so a flat coupon applied last is better for the shopper. It's worth checking the running total at checkout rather than assuming.
Working backwards from a sale price
- Original price from a sale price: divide by (1 − discount). $80 after 20% off means 80 ÷ 0.80 = $100 list.
- Discount percentage from two prices: (original − sale) ÷ original × 100.
- 'Buy one get one free' is a 50% discount across the two items, not 100% off.
- 'Buy two get one free' is 33.3% off, not 50% — you pay for two of three.
- 'Up to 70% off' signage usually means one item somewhere in the store is 70% off. Check the actual item.
Frequently asked questions
- Do two 20% discounts stack to 40% off?
- No — stacked percentage discounts compound. Two successive 20% discounts leave you paying 64% of the original price (a 36% total discount), not 60%.
- How do I find the original price from a sale price?
- Divide the sale price by (1 − discount rate). For a price of $80 after a 20% discount, divide by 0.80 to get the original $100.
- Can this calculate a discount from a percentage-off coupon and a flat-amount coupon together?
- Yes — apply each discount in the order they'd actually be applied at checkout to see the true final price.
- Is 'buy one get one free' the same as 50% off?
- In effect yes, provided you want both items. If you only need one, a straight 50% discount on a single unit is the better deal.
- Should the discount be applied before or after tax?
- Discounts are almost always applied to the pre-tax price, with tax then charged on the reduced amount. That works in your favour — the tax falls along with the price.
Read more on this
- Percentages, discounts and tax: the errors that cost moneyWhy stacked discounts never add up, how to pull tax out of an inclusive total correctly, and why a 20% rise isn't undone by a 20% fall.
- How GST works: slabs, forward vs reverse calculation, and input creditA clear guide to GST slabs, CGST/SGST vs IGST, extracting base price from gross invoices, and how input tax credit prevents cascading taxation.