Contribution margin

Revenue minus the costs that vary with each sale (discounts, delivery, payment fees). It shows what a sale contributes to fixed costs and profit.

FormulaContribution = revenue − costs that vary with each sale

Try it · 30 seconds · from Atterna’s practice

An AI assistant

“Paid orders totalled €552,645 in gross merchandise value (GMV).”

Can you infer the platform’s own revenue from that number?

Preparing the practice…

How we work it through

1
Start from what the platform earns, not from GMV.
2
Subtract what the promotion itself cost: discounts, extra delivery, fees.
3
Compare with a normal week before calling it a success.

On the practice dataset

The query we run on Meridian, Atterna’s practice marketplace, and what it returns.

-- commission minus platform discounts, by week
SELECT w.week_id,
  SUM(o.items_total_eur) AS gmv,
  SUM(o.items_total_eur * s.commission_rate)
    - SUM(o.platform_discount_eur) AS kept
FROM meridian.orders o
JOIN meridian.sellers s ON s.seller_id = o.seller_id
JOIN meridian.weeks w ON o.created_at >= w.week_start
                     AND o.created_at <  w.week_end
WHERE o.status = 'paid'
GROUP BY w.week_id;

Resultpromo week W38: GMV €230,967 (+54% on the two weeks before) but kept €4,961, against about €18,000 in each of those weeks

The common trap

Celebrating GMV growth from a promotion without checking contribution: sales can rise while the platform keeps less.

ExampleMeridian episode 1 starts from a promo week with GMV up 54% and asks what actually stayed with the platform.

When an AI answers

An AI assistant

“The promo was a success: GMV grew 54%.”

What it didn’t know: It was only given the GMV chart, not the discounts the platform paid for.
Ask back: “What did the platform keep in the promo week after its own discounts, compared with a normal week?”

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