A 20% sitewide discount doesn't cost you 20% — it comes straight off your margin, not your price. Enter your own numbers and the discount you're planning to see exactly how many more units you must sell just to make the same profit — and whether the promo can pay for itself at all.
| Per order | Full price | Discounted |
|---|---|---|
| Revenue Full price vs price after the discount | $0 | $0 |
| Product cost (COGS) Full price × COGS % — unchanged by a discount | −$0 | −$0 |
| Shipping & fulfillment The label, pick-pack and packaging you pay — the same either way | −$0 | −$0 |
| Payment fees % of the amount charged + fixed per-order fee | −$0 | −$0 |
| Contribution margin per order | $0 | $0 |
Contribution margin is what's left of an order after the costs that scale with it — product cost, shipping and payment fees. A discount lowers the revenue and the payment fee slightly, but the cost of the goods doesn't change. So a modest discount can take a big bite out of the margin that funds everything else. To break even on the promo, the extra volume has to replace the margin the discount gave away:
Example (the fields as they load): a $65 order with 35% COGS, $9 shipping and ~2.9%+$0.30 fees keeps about $31 of contribution margin. A 20% discount drops revenue to $52 while COGS and shipping hold, leaving about $18.40. Same profit now takes $31 ÷ $18.40 ≈ 1.7× the orders — you have to sell about 68% more units just to stand still. If the discount pushes the margin after to zero or below, no amount of volume can break even — the sale loses money on every order.
The break-even math above assumes the numbers you typed hold during the sale. During a promo they often don't: a supplier's price ticked up, a carrier surcharge landed, a 3PL sync fell behind and you oversold the discounted SKU, or payouts came in short against the spike in refunds. Each one lowers the "margin after" this calculator used — so the volume you actually needed was higher than planned, and you only find the gap after the sale is over.
Ops Monitor connects to your Shopify and Stripe with read-only API keys and watches for the silent operational failures that erode the margins a promo depends on — payout and settlement gaps, oversells, orders stuck past SLA, broken syncs — then alerts you by email or Slack the moment one shows up. It's read-only: it never writes to your store and never moves money. It detects and alerts — it does not prevent or guarantee anything.
Start monitoring in minutes with read-only keys — $149/month, self-serve, cancel anytime.
Start monitoring — $149/mo →Not ready? Run the free, no-signup Ops Reliability Scorecard, or get a one-time $29 ops audit of your store.