Contribution Margin Formula

Contribution margin is what each sale leaves over to cover fixed costs and profit, after subtracting the variable cost of making that unit. It is the single most useful number for pricing, break-even, and product-mix decisions.

The formula

The portion of sales revenue that exceeds variable costs. It contributes to covering fixed costs and profit.

What goes into it

• Revenue
• Cost of Goods Sold (COGS)

Worked example

Unit vs. total contribution margin

Unit contribution margin = price per unit − variable cost per unit. Total contribution margin = unit contribution margin × units sold. The contribution margin ratio expresses it as a percentage of price, which is handy when you sell many products at different prices.

When to use it

Use the unit contribution margin to find your break-even quantity (fixed costs ÷ unit contribution margin), to compare which products earn their keep, and to test whether a price change or a cost cut actually improves the bottom line.

Worked example: one Roomba, sold two ways

Chapter 23 of Tangibles prices a premium Roomba at $799.99 and puts the cost of producing one at $179.67. The book flags the production cost as an illustrative assumption; the list price was iRobot's own. Run those two numbers through the formula.

Step 1: sold direct. On irobot.com the company keeps the whole $799.99, so each robot contributes $620.32 towards fixed costs and profit. That is a 77.5% contribution margin ratio, and it is the number the rest of the business model is built on.

Step 2: sold through retail. Most Roombas are not sold direct. A big-box retailer typically keeps 30% or more of the shelf price. iRobot's revenue on the same robot drops to $559.99 while COGS stays at $179.67, so the contribution margin falls to $380.32, or 47.5% of what the retailer charged.

Step 3: read the gap. The same robot, the same factory, and the channel decision moves the unit margin by $240. Multiply by a year's volume and that is the marketing budget, or the reason a subscription such as iRobot Select looked tempting: $29 a month direct, with no retailer in between. Whether it beat the outright sale is the NPV question; whether the robot could be made and sold at a profit at all is this one, and here it clearly could.

When to use contribution margin, and when not

Use it to test a price before you commit to it, to find your break-even quantity (fixed costs divided by unit contribution margin), to compare which products in a range earn their keep, and to see what a channel, a discount or a cost-down does to the unit before it does anything to the business. For hardware, run it at each manufacturing mode: the $2.35 variable cost of a mass-manufactured part and the $10 of a small-series one give very different margins on the same price.

Do not use it as a proxy for profit. It ignores tooling, non-recurring engineering, certification, R&D, warranty reserves and every other fixed cost; a healthy contribution margin on a product that never reaches break-even volume is still a loss. Do not confuse it with gross margin either: gross margin follows accounting rules on what counts as cost of sales, contribution margin strips it to the variable cost of one more unit. And do not treat it as fixed. Component prices, freight and yields move it every quarter.

Frequently asked questions

Go further

• Chapter 20 of Tangibles builds the unit-economics toolkit: contribution margin, break-even, manufacturing mode, cost of capital and NPV.
• Break-even point via contribution margin: divide fixed costs by this number to find the volume you must sell.
• Profit formula: contribution margin at volume, less fixed costs.
• Manufacturing-mode crossover: how the variable cost, and so the margin, changes when you move from small series to mass production.
• Net present value: what a stream of contribution margins is worth today.

Related: all business formulas — the live directory includes NPV, contribution margin, customer lifetime value, and more.