Discount Calculator
Work out a sale price and how much you save, including stacked discounts — and see why 20% off then 10% off is not 30% off.
How to use this calculator
- 1Choose whether you want the sale price, the discount percentage, or the original price.
- 2Enter the two figures you know.
- 3For "extra X% off already reduced items", put the first discount in the main field and the extra in the stacked field.
How the calculation works
Sale price = Original × (1 − d₁) × (1 − d₂) Discount % = (Original − Sale) / Original × 100- Original
- The pre-discount price
- d₁, d₂
- Each discount as a decimal, applied in sequence
- Sale
- The price after all discounts
Stacked discounts multiply, they do not add. 20% then 10% is 0.8 × 0.9 = 0.72, which is 28% off, not 30%.
Reversing a discount requires dividing by (1 − d), not multiplying by (1 + d). A price cut by 20% must rise by 25% to get back to where it started.
Worked example
$120 with 25% off, then an extra 10%
- 1.First discount: 120 × (1 − 0.25) = $90.
- 2.Second discount applies to $90, not $120: 90 × (1 − 0.10) = $81.
- 3.Total saved is $39, which is 32.5% off — not the 35% you would get by adding the two percentages.
Result: $81, a 32.5% effective discount
Why businesses discount in the first place
A discount trades margin for something a business wants more urgently in that moment — usually speed. Cutting the price on slow-moving stock frees up cash and shelf space faster than waiting for a full-price buyer; a first-order discount gets a new customer to try something they might otherwise never sample; a seasonal sale clears inventory before it goes out of fashion or out of date. Used well, a discount is a deliberate trade of some profit now for a faster sale, a new customer, or emptier shelves — not simply giving money away.
Common types of discounts
Retailers reach for a discount for different reasons, and the type usually signals which one.
- Clearance and seasonal sales — reducing prices to move stock before it becomes unsellable — out-of-season clothing, perishable goods, last year’s model.
- Volume discounts — a lower unit price for buying more, which rewards the customer for reducing the seller’s per-order handling cost.
- Loyalty and repeat-customer discounts — aimed at retention rather than a single sale, betting that a small discount now earns a larger lifetime relationship.
- Flash sales and limited-time offers — using urgency and scarcity to pull forward demand that might otherwise have waited or gone to a competitor.
- Coupons and promo codes — let a business discount selectively — only for shoppers motivated enough to seek out or redeem the code — rather than cutting the price for everyone.
Why stacked discounts add up to less than they look
When two discounts apply one after another, the second is calculated on the already-reduced price, not the original one — so a 20%-off sale followed by an extra 10% off is not 30% off, it works out closer to 28%. The gap between what stacked discounts appear to offer and what they actually deliver grows with every additional discount layered on, which is part of why "extra X% off already-reduced items" promotions feel more generous than the maths behind them actually is.
The risks of discounting too often
A discount that moves slow stock or wins a new customer is doing its job; a discount that becomes routine can quietly work against the business offering it.
- Margin erosion — every discount comes directly out of profit, and frequent discounting can turn a healthy margin into a thin one without any single decision looking reckless.
- Anchoring customers to the sale price — shoppers who get used to buying only during sales start treating the discounted price as the real one, making full-price sales harder to achieve later.
- Brand devaluation — constant discounting can signal that the regular price was never a fair one, undermining trust in the pricing itself.
- Training customers to wait — if sales are frequent and predictable, some buyers simply delay purchases until the next one, which can hollow out full-price revenue.
Spotting a discount that is not what it looks like
From a shopper’s side, a percentage off is only meaningful relative to a genuine starting price — a "50% off" tag means little if the original price was inflated first. Checking a price history, comparing against other retailers, and reading exactly what the discount applies to — the listed price, or a price after other fees — are the simplest ways to tell a real saving from a marked-up "was" price designed to make the discount look larger than it is.
What this assumes, and where it stops
Assumptions
- Discounts are applied in the order entered.
- Prices exclude sales tax or VAT, which is normally calculated on the discounted amount.
Limitations
- Does not handle fixed-amount vouchers, buy-one-get-one offers, or minimum-spend thresholds.
- Where tax is included in the displayed price, the saving on the tax-exclusive amount will differ slightly.
Common questions
Why is 20% off plus 10% off not 30% off?
Because the second discount is calculated on the already-reduced price. On a $100 item, 20% off gives $80, then 10% off $80 is $8, not $10 — so you pay $72 and save 28%. Stacked discounts always come to less than the sum of their percentages.
A price dropped 20%. What increase brings it back?
25%. Going down 20% from 100 gives 80; going back to 100 from 80 requires adding 20, which is 25% of 80. Percentage decreases and increases are not symmetric because the base changes.
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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