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Lightning Deal and Coupon Impact Calculator

A promotion is worth running only if it earns more than the profit you would have made without it. This calculator compares two worlds: a baseline in which you sell your normal volume at your normal price, and a deal window in which you sell a larger volume at a discounted price, pay a fixed Lightning Deal or coupon fee, and give up the full-price margin on every unit that would have sold anyway. The difference between those two numbers is the only figure that matters, and it is frequently negative. Enter your own numbers below; the fields load with a worked example already filled in.

Published August 31, 2026 · Last reviewed August 31, 2026 · This is an estimator for planning. Confirm the current deal fee, coupon redemption fee, and your category referral rate in Seller Central before you schedule a promotion.

Calculate the profit impact of a deal

Your everyday price, before tax.

Percentage off the normal price during the window.

Fixed event fee, or redemption fee times expected redemptions.

Landed cost plus fulfillment, storage, advertising, and returns reserve.

Category rate, commonly 8-15%.

Baseline demand at full price, from a comparable recent period.

Total units sold during the window, baseline included.

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How the deal impact calculation works

The model is a comparison, not a single margin figure. It builds the two scenarios separately and subtracts one from the other, so the answer is always framed against the alternative of doing nothing:

  1. Deal price = normal price × (1 − discount rate). This is the price the buyer pays during the window, and every downstream figure keys off it.
  2. Profit per unit at the normal price = normal price − (normal price × referral rate) − all-in unit cost. The all-in cost is everything except the referral fee: landed product cost, fulfillment, allocated storage, advertising per unit, and any returns reserve.
  3. Profit per unit at the deal price = deal price − (deal price × referral rate) − all-in unit cost. The referral fee shrinks with the price, which is the only cost that moves in your favor. Every other cost is unchanged, which is why the discount lands almost entirely on your margin.
  4. Baseline profit for the window = profit per unit at the normal price × units you would have sold anyway. This is the profit you are giving up to run the promotion, and it is the number most deal analyses omit.
  5. Deal profit for the window = profit per unit at the deal price × units expected at the deal price − the fixed deal fee. Note that the deal units figure is the total for the window, so it already contains the baseline units, now sold at a discount.
  6. Incremental result = deal profit − baseline profit. Positive means the promotion paid for itself. Negative is the amount it cost you relative to leaving the listing alone.
  7. Break-even volume = (baseline profit + deal fee) ÷ profit per unit at the deal price. This is the number of discounted units required to get back to the profit you would have made anyway. When the profit per unit at the deal price is zero or negative, no volume reaches break-even and the calculator says so rather than printing a meaningless number.

Two properties of this arithmetic drive nearly every bad deal decision. The first is that the deal fee is fixed and the per-unit economics are variable, so the fee is almost never the problem. A $150 event fee spread over 400 units is $0.38 per unit; a discount that pushes the unit into negative contribution is unbounded, because it grows with every sale. The sign of the profit per unit at the deal price decides whether volume is your friend or your enemy, and it decides that before you have sold a single unit.

The second is cannibalization: the units that would have sold at full price regardless. Those buyers were already going to convert, and the promotion simply handed them a discount. If your baseline is 120 units and the deal moves 400, only 280 units are genuinely incremental, but all 400 carry the reduced margin. Sellers who compare deal-window revenue against a quiet week, rather than against the profit the same week would have produced on its own, systematically overstate what promotions earn.

Set the discount against the break-even price for the SKU, which you can compute on the FBA profit calculator. If the deal price sits below that figure, you are selling below cost, and the honest question is not whether the deal is profitable but whether the loss is buying something worth the money.

Worked example: a 20% deal on a $24.99 SKU

These are the values the calculator loads with, so you can see the method and the widget agree. Figures are illustrative.

  • Normal price $24.99, discount 20%, deal fee $150.00, all-in unit cost excluding referral $17.32, referral rate 15%, baseline 120 units, expected deal volume 400 units.
  • Deal price: $24.99 × 0.80 = $19.99.
  • Profit per unit at the normal price: $24.99 − $3.75 − $17.32 = $3.92.
  • Profit per unit at the deal price: $19.99 − $3.00 − $17.32 = -$0.33, a loss on every unit sold.
  • Baseline profit: $3.92 × 120 = $470.58.
  • Deal profit: (-$0.33 × 400) − $150.00 = -$280.72.
  • Incremental result: -$280.72 − $470.58 = -$751.30. Break-even volume: not achievable at any volume.

This scenario is deliberately a losing one, because it is the shape of deal that gets scheduled most often. The break-even price on this SKU is $20.38, so a 20% discount to $19.99 sells below cost from the first unit. Selling 800 units instead of 400 would roughly double the negative contribution, not recover it. The fee is the small part of the damage: cannibalizing 120 full-price units costs $470.58 on its own, more than three times the $150.00 event fee.

When a losing deal is still the right call

Running a promotion at a loss is a legitimate tactic in three situations, provided the loss is deliberate and budgeted rather than accidental. The first is rank acquisition, where a burst of velocity lifts organic position on a target keyword and the gain persists after the price returns to normal. The second is inventory clearance, where units are approaching an aged inventory surcharge or a fourth-quarter peak storage rate, and paying a small loss now avoids a larger carrying cost later, as modelled on the storage and aged inventory calculator. The third is launch velocity, where early sales and reviews are worth more than the margin sacrificed to get them.

In all three cases, the discipline is the same: decide the maximum acceptable loss before scheduling, treat that figure as a marketing or clearance line in the budget, and check afterward whether the intended benefit actually arrived. A deal that loses $751.30 to buy rank is a defensible investment if rank was the goal and rank was gained. The same deal run because the discount looked modest is simply a mistake that took six weeks to appear in a settlement report.

Frequently asked questions

Why does selling more units in a deal sometimes increase the loss?

Because the deal fee is fixed but the per-unit economics are not. If every discounted unit earns a positive contribution, extra volume dilutes the fee and the deal improves as it scales. If the discounted price falls below your break-even price, every additional unit adds another small loss on top of the fee, so volume makes the result worse rather than better. Check the sign of the profit per unit at the deal price before you look at anything else.

What is cannibalization and how do I estimate it?

Cannibalization is the share of deal units that would have sold at full price anyway, so the discount on them buys you nothing. Estimate it from the trailing four weeks of units sold in a comparable window, adjusted for seasonality, and enter that figure in the baseline field. Sellers who ignore it consistently overstate deal performance, because the promotion gets credit for demand it did not create.

Is it ever right to run a deal that loses money?

Yes, when the loss buys something you actually need: search rank on a launch, velocity ahead of a competitive window, or clearing aged units before a long-term storage or aged inventory surcharge lands. The discipline is to size the loss in advance and treat it as a marketing or clearance budget line rather than discovering it in a settlement report six weeks later.

How is a coupon different from a Lightning Deal in this model?

The structure is the same and the model handles both. A Lightning Deal or Best Deal carries a fixed fee per event, while a coupon carries a redemption fee charged per unit redeemed. For a coupon, multiply the per-redemption fee by the units you expect to redeem and enter that product in the deal fee field, then read the result the same way.

Should the referral fee be recalculated at the deal price?

Yes, and this calculator does it. The referral fee is a percentage of the price the buyer actually pays, so a lower price lowers the fee proportionally. That partial offset is real but small: a 15% referral rate returns only $0.15 of every dollar you discount, which is why a 20% price cut never costs anything close to 20% of profit.

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