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Glossary
Contribution margin
Contribution margin is revenue minus the variable costs relevant to the chosen unit and analysis horizon — the amount available to cover fixed costs and profit. It can be expressed in currency or as a percentage of revenue and is foundational to unit economics. Relevant-cost classification depends on the decision; financial-statement COGS is not an automatic definition of variable cost.
Why it matters
Gross margin and contribution margin are often blurred. Contribution margin focuses on costs that change with the unit of analysis over the horizon being decided (for example incremental hosting, payment fees, or variable support). Misclassifying fixed costs as variable — or treating every COGS line as variable for every decision — produces false confidence.
Operators should state what is included for their model and unit. Marketplace take-rate businesses, SaaS, and physical goods will count different lines. Contribution margin is necessary but not sufficient: fixed opex, CAC, and cash timing still determine survival.
Example (enterprise): A usage-based API product prices so that after incremental inference costs and payment fees, contribution margin per call remains positive at expected utilization — then designs packaging so average customers cover CAC within a target payback window.
Mechanisms
- Relevant-cost definition — identify costs that change with the unit for the decision and horizon.
- Margin calculation — revenue − those variable costs (absolute and percentage).
- Decision use — pricing floors, product mix, and whether incremental growth helps or hurts.
Boundaries
- Contribution margin ≠ gross margin in every accounting system; COGS vs variable opex classifications can differ.
- Not every COGS item is variable for every unit decision; not every variable cost appears in COGS.
- Contribution margin ≠ profit after fixed costs and overhead.
- High contribution margin does not justify unlimited CAC spend without payback discipline.
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