Free tool Discount calculator for prices and promotions
Enter a price and a discount to get what the customer pays and what they save. Switch to stacked discounts, “buy 2, second half price”, “spend $100, save $20” or a reverse lookup from two prices. Add your unit cost and it tells you the margin after the discount and how many more units you would have to sell to earn the same gross profit.
- Five promotion types
- Margin and sales lift after discount
- Runs locally
What does the customer pay, and what does it cost you?
Choose the promotion, then fill in the price and the deal. Cost is optional; with it you see the margin side.
Percent off (20 = 20% off) or the Chinese “zhe” convention (8 = pay 80%).
Unit price; for spend-and-save, the basket total.
Percent off, e.g. 25.
Applied first, e.g. 20.
Applied to the already reduced price, e.g. 10.
Buy 2, second half price → 2.
Buy 2, second half price → 1.
50 = half price; 100 = free.
The threshold, e.g. 100.
Money off when the threshold is met, e.g. 20.
What the customer actually pays.
Same basis as the price: unit cost, or the basket’s cost for spend-and-save.
Customer pays
$60.00
For the whole deal
Equivalent “zhe”
7.5
Share of the original price paid, in tenths
Effective discount
25.0%
Money saved ÷ original price
Share these inputs: the values go after the # in the link, so they never reach a server.
https://tapcub.com/tools/discount-calculator
Version v1.0Updated Update history
What the numbers tell you
The sale price is the easy part. The margin lines tell you whether the promotion can pay for itself.
Customer pays
The price after every rule is applied, for the whole deal. For BOGO it is the total for all items, with the average per item below it.
Effective discount
Money off ÷ original price. It is the number to compare deals with: “second half price” and “25% off” cost you the same on a pair.
Gross margin after
What is left of each sale after the cost of the product. A discount comes straight out of margin, so a 20% discount on a 40% margin halves the profit per unit.
Extra units needed
How many more units you must sell, compared with no promotion, to make the same gross profit. 100% means twice the volume.
We do not publish typical sales lifts for promotions: they depend on the product, the audience and the season. Measure your own baseline and promotion periods.
Price a promotion in four steps
Start with the deal the shopper sees, then look at what it costs you.
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1
Pick the promotion type
One discount, two stacked, BOGO, spend-and-save, or reverse from a sale price.
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2
Enter the price and the deal
Use the price before any discount and the exact rule from your promo copy.
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3
Add your unit cost
Landed cost per unit, or the basket’s total cost for spend-and-save.
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4
Compare against the lift
If the extra units needed look unrealistic, try a smaller discount or a threshold instead.
Sale price = original price × (1 − discount)
Every promotion type reduces to the share of the original price the customer pays. The margin check compares profit per unit before and after.
- Stacked: pay share = (1 − d₁) × (1 − d₂). 20% then 10% = 0.8 × 0.9 = 0.72, i.e. 28% off
- Buy N, get M at d off: effective discount = M × d ÷ N. Buy 2, second half price = 1 × 50% ÷ 2 = 25%
- Spend X, save Y: discount = Y ÷ basket total, deepest exactly at X
- Extra units needed = (price − cost) ÷ (sale price − cost) − 1
- Comparison prices are regulated: in the EU the “was” price must be the lowest price of the previous 30 days (Omnibus Directive (EU) 2019/2161); in the US, 16 CFR Part 233 requires a genuine former price
One discount
price × (1 − d)
$80 × (1 − 25%) = $60
Stacked
price × (1 − d₁) × (1 − d₂)
$80 × 0.8 × 0.9 = $57.60 (28% off)
Buy 2, 2nd half price
1 − (1 × 50%) ÷ 2
75% paid, 25% off
Spend $100, save $20
20 ÷ basket
$100 basket: 20% off; $160 basket: 12.5% off
Extra units needed
(P − C) ÷ (P′ − C) − 1
($80 − $32) ÷ ($60 − $32) − 1 = 71.4%
A $80 jacket at 25% off
The jacket costs $32 to land, a 60% gross margin. The store wants to run 25% off and is weighing it against “buy 2, second half price”.
| Step | Calculation | Result |
|---|---|---|
| Sale price | $80 × (1 − 25%) | $60.00 |
| Margin before | ($80 − $32) ÷ $80 | 60.0% |
| Margin after | ($60 − $32) ÷ $60 | 46.7% |
| Extra units needed | $48 ÷ $28 − 1 | 71.4% |
| BOGO half price, per pair | $80 + $40 | $120 (25% off) |
| BOGO margin per pair | ($120 − $64) ÷ $120 | 46.7% |
Both promotions give the same 25% discount and the same margin. The difference is that BOGO only pays out when the customer buys two, which raises units per order.
Where promotion math goes wrong
Most discount surprises come from adding percentages or forgetting the cost side.
Adding stacked discounts
20% off plus an extra 10% off is 28%, not 30%. The second discount applies to an already reduced price.
Calling BOGO half price “50% off”
“Second item half price” is 25% off the pair. Advertise it as 50% off and you overstate the deal.
Judging a promo by revenue
Revenue can rise while gross profit falls. Check the extra units needed against what the promotion realistically brings.
An inflated “was” price
In the EU the reference price must be the lowest of the last 30 days; in the US the former price must be genuine. Use the real regular price.
See what the promotion actually sold
TapCub does not know your costs, but it measures the order side of a promotion from your purchase and refund events.
GMV, AOV and refund rate
The ecommerce template computes GMV, average order value, checkout completion and refund rate from purchase and refund events.
Learn moreCoupon as a property
begin_checkout carries the coupon when one is used, so the purchase funnel can be split by coupon.
Learn moreDid discount buyers come back?
Repeat-purchase retention by week shows whether promotion buyers return at full price.
Learn moreDiscount questions
Still have a question?
Chat with the team behind TapCub — we usually reply within a few hours on business days.
How do I calculate a discount?
Multiply the original price by (1 − discount). 25% off $80 is $80 × 0.75 = $60. The saving is $80 − $60 = $20.
How do I calculate the percent off from two prices?
Divide the saving by the original price: ($80 − $59) ÷ $80 = 26.25% off. Switch the calculator to “find the discount from two prices”.
Are two discounts added together?
No. They multiply: 20% off and then 10% off leaves 0.8 × 0.9 = 72% of the price, a 28% discount. The order does not matter.
What discount is “buy one, get one half price”?
On a pair it is 25%: you pay 1.5 items for 2. “Buy one, get one free” is 50% off the pair; “buy 2, get 1 free” is 33.3% off three items.
How much more do I need to sell when I discount?
Divide the margin per unit before by the margin per unit after, and subtract 1. At a 40% margin, a 20% discount needs 100% more units to make the same gross profit; a 10% discount needs 33%.
Is “spend $100, save $20” the same as 20% off?
Only for a basket of exactly $100. At $160 it is 12.5% off, and below $100 it is nothing. Thresholds are usually used to lift basket size.
What can I show as the original price?
In the EU, a price reduction must show the lowest price of the previous 30 days. In the US, the FTC pricing guides require that the former price was genuinely offered for a reasonably substantial period. Check local rules before running a promotion.
Update history
New features, fixes and data refreshes for this tool, newest first.
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· v1.0
LaunchedFirst release.
Missing something or found an error? Tell us — requests that come up often go into the next update. All tool updates
Measure the promotion, not just the price
Connect your store to see orders, AOV, coupon use and refunds per promotion, and whether those buyers return.