Contribution Margin and Break-Even: From One Sale to Fixed-Cost Coverage

Contribution margin answers a practical question: how much of each sale remains to pay fixed costs? Once that amount is known, a break-even calculation translates fixed costs into the sales volume needed to cover them. The method is simple, but its assumptions matter.

Calculate contribution per unit

An item sells for $50 and incurs $30 of variable costs. Contribution is $20 per unit, and the contribution ratio is $20 ÷ $50 = 40%. Variable costs should include costs that change with the sale under your model, such as product cost and relevant per-order charges.

Contribution is not net profit. If monthly fixed costs are $6,000, the first $6,000 of contribution goes toward those costs before the model shows a profit.

Find the break-even point in units and revenue

Break-even units = fixed costs ÷ contribution per unit. Here, $6,000 ÷ $20 = 300 units. At $50 each, that is $15,000 revenue. The revenue approach gives the same answer: $6,000 ÷ 0.40 = $15,000.

When the unit calculation is fractional, round up. If fixed costs were $6,010, the theoretical result would be 300.5 units. Selling 300 units would leave a shortfall, so 301 whole units are required.

Understand the stable-cost assumption

The calculation assumes price and variable cost remain constant over the relevant range. Discounts can reduce contribution, while a larger order may reduce unit purchasing costs. A new warehouse or employee may introduce a step increase in fixed costs.

If selling price equals variable cost, contribution is zero and no finite number of units covers positive fixed costs. Selling more of that product does not solve the problem within this model.

Handle more than one product carefully

Suppose product A contributes $20 and product B contributes $10, and the expected unit sales mix is 60% A and 40% B. Weighted contribution is 0.60 × $20 + 0.40 × $10 = $16 per unit. At $6,000 fixed costs, the model needs 375 units at that mix.

Those 375 units would be 225 of A and 150 of B, contributing $4,500 plus $1,500. If customers buy more of the lower-contribution product, the original break-even volume no longer holds.

Run the calculation

Start with the Contribution Margin Calculator, then use Break-Even Units or Break-Even Revenue. Keep fixed costs and sales targets on the same time basis.

Related reading

Continue with Target Profit Planning: How Many Units Must You Sell? for another part of the calculation.