Contribution margin drives everything
Each unit sold contributes its price minus its variable cost toward the fixed costs. Break-even is simply fixed costs divided by that contribution. Once you pass it, every further unit's contribution is profit.
This is why raising price or cutting variable cost moves break-even far more than cutting fixed costs does. If contribution is 200 on a 500 price, a 10% price rise adds 50 to contribution — a 25% improvement that pulls break-even down by a fifth.
Margin of safety
Break-even tells you the floor; the margin of safety tells you how much room you have above it. If you break even at 250 units and expect to sell 400, your margin of safety is 150 units, or 37.5% — sales could fall by that much before you start losing money.
A thin margin of safety means small demand shocks turn into losses. It is the number to watch when fixed costs are high relative to contribution, because those businesses have little cushion.
Operating leverage cuts both ways
A business with high fixed costs and low variable costs — software, hotels, airlines — has high operating leverage. Past break-even, almost every additional sale is profit, so profits rise sharply with volume. Below it, losses mount just as fast.
Low operating leverage, where most costs are variable, produces flatter results in both directions. Neither is inherently better; they suit different levels of demand certainty.
Frequently asked questions
What counts as a fixed cost? +
Anything you pay regardless of how much you sell: rent, permanent salaries, software subscriptions, insurance. Materials, shipping and payment processing are variable.
What if I sell several products? +
Use a weighted average contribution margin across your actual sales mix. The break-even figure then holds only as long as that mix does.
Should owner salary be a fixed cost? +
If you need to be paid, yes — include it. Break-even calculated without paying yourself understates what the business must actually earn to be viable.