The formula
Given percent discounts d₁, d₂, …, dₙ each expressed as a decimal, the effective combined discount is 1 − (1 − d₁)(1 − d₂)…(1 − dₙ). The widget evaluates that product directly.
Discount Calculator
Single or stacked discounts, with the effective rate clearly broken out.
The trap with stacked discounts is assuming they add: 20% off plus another 10% off is not 30% off. The second discount applies to the already-discounted price, so 20% + 10% stacked is actually 28% effective. The calculator below makes the stacking explicit — add up to four discount layers and the effective combined rate shows in the result.
%
Savings
$20.00
Sale price
$60.00
Effective discount
25.00%
How to use
Enter the list price
The pre-discount sticker price.
Add discount layers
Start with one percent off. Tap "Stack another" to add more — coupon-on-coupon stacks, or store-discount + member-discount.
Read the effective rate
The right-most stat shows the equivalent single-discount percentage. Use it to compare offers like "50% off" vs "40% off, then 15% off".
Common stacking outcomes
| Stack | Naïve sum | Actual effective |
|---|---|---|
| 20% + 10% | 30% | 28% |
| 50% + 20% | 70% | 60% |
| 30% + 30% | 60% | 51% |
| 25% + 25% + 10% | 60% | ~49.4% |
Frequently asked questions
- Why don't stacked discounts add?
- Each discount applies to the running price, not the original. 20% off $100 is $80; another 10% off $80 is $72, not $70. The savings against the original were $28 — an effective 28% discount.
- Does the order of discounts matter?
- Mathematically no — multiplication is commutative. 20%→10% and 10%→20% both reach $72. Stores may impose constraints (e.g., member discount applies first, then promo) but the math doesn't care.
- What's the difference between stacking and adding a coupon?
- If the coupon is "$10 off" it's not a percentage — apply it after the percentage discounts. If it's another percent, it stacks multiplicatively.
- Does the calculator store my data?
- No. Every computation runs in your browser.
About
Why this matters
Retailers occasionally advertise stacking offers as if they were additive. They're not — and a 50% off + 20% off promotion is 60% effective, not 70%. Useful to know before you commit to a basket.