E-commerce discounts: when they pay off and when they destroy your margin

The problem with discounts nobody tells you about

A 20% discount looks small. But if your gross margin was 35%, that 20% ate more than half of your profit — and that's before adding shipping costs, Mercado Pago fees, operating costs and the ad spend that drove the sales.

The right question isn't "how much did I sell in the promo?" but "how much did I make?" And the answer is almost never what the founder expects.

To understand why, you first need to be clear on your real margin — not a rough gross figure, but the margin after every cost. You can see how to calculate it in our article on contribution margin in e-commerce.

How much does a discount really destroy?

Let's take a concrete example. You have a product that sells for $10,000. Your cost is $5,000. Gross margin: 50%.

If you run a 30% discount, you now sell at $7,000. But the cost is still $5,000. Your margin went from 50% to 28.5%. And that still doesn't count:

• The Mercado Pago fee (between 3.5% and 6.5% depending on the payment method — see the full breakdown)
• The shipping cost that the seller often absorbs during promos
• The Meta Ads spend to push the offer
• Interest-free installments, which take 8% to 12% off the amount you receive
• The agency fee, if you work with one

Add it all up and that "30% off" can leave you with a negative net margin. You're selling at a loss and sales volume doesn't make it back — on the contrary, it makes it worse. Every additional sale is an additional loss.

The hidden costs of e-commerce are exactly these — the ones that don't show up in the promo spreadsheet but eat your margin anyway.

Why a "rough margin" isn't enough to decide

Most founders have a rough idea of their margin. But that idea doesn't include every cost. What gets left out of the typical spreadsheet before a promo:

• The real cost of installments (which varies by card and by bank)
• Mercado Libre fees by product category
• The cost of shipments that came back without a sale
• The cost of refunds and returns, which always go up during promos
• The real ad spend attributable to each sale — not the month's total budget

When you calculate margin with incomplete data, the result always looks better than it is. And when you run a promo on that inflated margin, the damage is bigger than you expected.

When does a discount make sense?

Not every discount is a trap. There are situations where it makes real financial sense:

• Clearing dead stock. A product that doesn't move has a huge opportunity cost: it takes up space, ties up capital and generates storage costs. An aggressive discount to move it can free up capital worth more than the margin you give up.
• Acquiring new customers with high LTV. If you know a customer buys 4 times a year at an average margin of $X, giving up margin on the first purchase can be an investment that pays back. But you need the LTV figure to calculate it — without that number, it's a bet.
• Selective promos on high-margin products. Not across the whole store, but on the specific products where margin before costs is above 60-70%. That's where you have room to absorb the discount and stay profitable.
• Seasons when the market expects a discount. During Hot Sale or CyberMonday, not discounting can be worse than discounting badly — the traffic goes to the competition. But the discount has to be surgical, not a store-wide promo with no analysis.

The calculation you should run before every promo

For every product you'll include in the promo, you need to calculate the net margin with the discount applied. The formula:

Ad spend per sale is the hardest number to calculate. An approximation: if you spend $50,000 on ads and generate 100 sales, the ad cost per sale is $500. If the margin on each sale after all costs is $400, you're losing $100 per sale.

Escalafy runs this calculation automatically, in real time, by product and by order. No waiting until month-end to find out the promo was a loss.

How Escalafy helps you decide what to discount and by how much

Escalafy's profitability by product module shows you the real margin of each SKU including every cost: cost of goods, Tiendanube fees, Mercado Pago fees, shipping, discounts and the ad cost that generated that sale. In real time.

Before launching a promo, you can see which products have enough margin to absorb the discount and which don't. You can work out: if I cut the price 20%, how many units do I need to sell for total profit to beat what I'd make without the discount?

During the promo, you see in real time whether each order is profitable or loss-making. You don't wait until month-end to discover you sold a lot and made little.

And afterward, you can compare the profitability of the promo week vs. normal weeks. Did it generate more total profit or just more volume at a lower margin? That comparison tells you whether the promo was worth it — and how to adjust the next one.

FAQ about discounts and margin in e-commerce

How big a discount can I run without losing money?

It depends on your gross margin. If you have a 50% margin, you can discount up to 30% and keep a positive gross margin — but that's before shipping, fees and ads. With every cost included, the break-even point is usually 10-15 points higher than it looks. With a 40% margin, a 20% discount can already put you in the red if your operating costs are high.

Is a "buy one, get one free" better than a percentage discount?

Buy one, get one free has more psychological impact than "50% off," but mathematically they're nearly equivalent. The real difference is the logistics cost of the second item: if shipping two products instead of one costs significantly more, the 2-for-1 can be worse than the percentage discount, even if it's perceived as more attractive.

When is it better not to discount?

When your demand is already at the limit of your operating capacity, when the costs of scale (logistics, customer service) exceed the extra benefit, or when the product's margin is under 35% and you already carry significant ad and fee costs. Also when the brand is positioned on quality — frequent discounts erode perceived value.

How do I measure whether a promo worked?

Not by sales volume or revenue. By the period's total net profit compared with equivalent periods without a promo. If you sold three times as much but your net profit was lower than in a normal week, the promo wasn't a success — it was a loss dressed up as a sales record.

Are discount coupons better than store-wide promos?

Generally yes, because they let you segment: send the coupon only to customers who haven't bought in 90 days, or to those who bought once and never came back. That limits the damage to your margin — you're not giving a discount to people who were going to buy anyway. But they need the same upfront margin analysis: if the coupon puts the sale in the red, the segment doesn't matter.

Do peak seasons always justify discounts?

No. The "you have to discount during Hot Sale" argument holds if you don't want to lose traffic, but not for running just any discount. In peak season, buyers are willing to pay — the discount is there to compete, not to capitulate. A strategic 10-15% on the products whose margin allows it is very different from 40% across the whole store.