How Discounts Affect Profit Margin: Break-Even Sales Lift for Promos

20% off is not 20% less profit

A discount comes off revenue, not just profit. If a product has a 40% contribution margin and you discount it by 20%, you may have cut the actual per-order profit in half or worse.

Profit before discount

profit_before_discount = normal_price - COGS - shipping - packaging - fee_before

Profit after discount

discounted_price = normal_price * (1 - discount_percent)
profit_after_discount = discounted_price - COGS - shipping - packaging - fee_after

Required sales lift

units_required_to_match_old_profit = profit_before_discount / profit_after_discount
required_sales_lift = units_required_to_match_old_profit - 1

If profit after discount is zero or negative, no realistic conversion lift saves the promo. You are making the loss faster. Athletic, but dumb.

When discounts are useful

Discounts can make sense for clearing inventory, acquiring customers with high repeat value, increasing AOV, or moving seasonal stock. They get dangerous when the only plan is "more orders will fix it" and nobody checks the math.

Use the Discount Damage Calculator before launching the promo.