How to Calculate Break-Even (and Why Contribution Margin Is the Number That Runs the Business)

The problem: you're pricing a product at $40 and don't know if you'll ever make money

You sell a widget for $40. Materials and labor cost $15 per unit. Rent, salaries, and insurance come to $10,000 a month. You sell 300 units a month — is that enough? Revenue is $12,000, variable costs are $4,500, fixed costs are $10,000, and profit is -$2,500. You're losing money. How many units do you need to sell to stop losing it? The instinct is to divide total costs by price ($14,500 / $40 = 362.5) — but that's wrong because it treats variable cost as if it doesn't scale with units. The honest move is one division: fixed costs ÷ contribution margin per unit, where contribution margin is price minus variable cost. $10,000 ÷ ($40 − $15) = 400 units. At 400 units you break even. At 300 you lose $2,500. At 500 you make $2,500. The rest of the business is detail.

Fastest path

Open the Break-Even Calculator, type fixed costs, variable cost per unit, price per unit, read the result.

Fixed Costs:          $10,000
Variable Cost/Unit:   $15
Price/Unit:           $40

→ Contribution Margin/Unit:    $25  (price − variable cost)
→ Contribution Margin Ratio:   62.50%  (margin ÷ price)
→ Break-Even Units:            400
→ Break-Even Revenue:          $16,000
→ 50% of BE:    200 units  · revenue $8,000   · profit −$5,000 (loss)
→ 100% (BE):    400 units  · revenue $16,000  · profit $0
→ 150% of BE:   600 units  · revenue $24,000  · profit $5,000
→ 200% of BE:   800 units  · revenue $32,000  · profit $10,000

The tool took three inputs, computed one division (FC / (P − VC)), and rendered four profit/loss scenarios at 50%, 100%, 150%, and 200% of the break-even unit count. The rest of this guide is why contribution margin not gross margin is the number that runs the business, why price below variable cost means no break-even exists, why the 50% scenario is always a loss, and why fixed costs are only fixed below a capacity ceiling.

The substance: one division, four scenarios, one warning

The formula is one division

Break-even units = fixed costs ÷ (price − variable cost per unit). That's it. The denominator, price − variable cost, is the contribution margin per unit — the amount each unit "contributes" toward covering fixed costs. Sell one unit at $40 with a $15 variable cost and you've contributed $25 toward the $10,000 of fixed costs. Sell 400 and you've contributed exactly $10,000 — every dollar of contribution past 400 units is profit. The tool's breakEvenUnits = FC / contributionMargin is this division. Break-even revenue is just breakEvenUnits × P — the revenue you'd book at the break-even unit count.

The contribution margin ratio is the same idea expressed as a percentage of revenue: contributionMargin / P × 100. The tool computes it as (P - VC) / P * 100 — for our example, 25 / 40 × 100 = 62.50%. This tells you that 62.5 cents of every revenue dollar goes toward fixed costs (and then profit). A 62.5% contribution margin ratio means a $1,000 sale contributes $625 to fixed-cost coverage. The ratio is useful when you think in revenue instead of units — for service businesses with no clean "unit," break-even revenue = fixed costs ÷ contribution margin ratio.

Contribution margin, not gross margin

Gross margin and contribution margin are different numbers that both get called "margin," and the confusion costs money. Gross margin = revenue − cost of goods sold, where COGS includes both variable costs and an allocated share of fixed manufacturing overhead. Contribution margin = revenue − variable costs only — fixed costs are excluded and treated as a lump below the line. The difference matters because gross margin spreads fixed costs across units (so each unit's gross margin shrinks as you produce less), while contribution margin treats fixed costs as a block that has to be covered once, not per-unit.

The break-even formula only works with contribution margin. If you plug gross margin into FC / grossMarginPerUnit, you double-count fixed costs — once inside gross margin, once as FC. The tool's formula uses price minus variable cost, which is contribution margin, not gross margin. If you're pulling numbers from an income statement, use the variable cost line (materials, direct labor, shipping, commissions) — not COGS, which includes fixed manufacturing overhead.

The warning: price below variable cost has no break-even

The tool's hasBreakEven = contributionMargin > 0 && FC >= 0 is the guard. If P ≤ VC, the contribution margin is zero or negative — every unit sold loses money before fixed costs are even considered. There's no unit count that recovers fixed costs because each unit adds to the loss. The tool renders a yellow warning: "Your price per unit must be greater than your variable cost per unit. Otherwise each unit sold loses money, and fixed costs can never be recovered."

This is the "sell at a loss and make it up on volume" trap. It doesn't work. If you sell at $15 with a $15 variable cost, you contribute $0 per unit — you'd need infinite units to cover $10,000. If you sell at $10 with a $15 variable cost, each unit adds $5 to the loss — 400 units puts you at -$12,000 instead of $0. The fix is never more volume; the fix is raise price, cut variable cost, or stop selling the product.

The four scenarios and why 50% is always a loss

The tool renders four scenarios at 50%, 100%, 150%, and 200% of the break-even unit count. The 50% scenario is always a loss, and the math is exact: at 50% of break-even units, you've contributed 0.5 × FC toward fixed costs, so profit is 0.5 × FC − FC = -0.5 × FC. For our example: 200 units × $25 contribution = $5,000; fixed costs are $10,000; profit is -$5,000. Exactly half the fixed costs, lost.

The 100% scenario is always exactly zero by definition — that's what break-even means. The 150% scenario is always a profit of 0.5 × FC — the mirror of the 50% loss. The 200% scenario is always a profit of FC — one full fixed-cost block, earned. This linearity is the whole point of CVP (cost-volume-profit) analysis: profit is a linear function of units above break-even, and the slope is the contribution margin per unit. Double the units above break-even, double the profit.

Fixed costs are only fixed below a capacity ceiling

The formula assumes fixed costs don't change with output. This is true within a relevant range — the range of output your current capacity can handle. The $10,000 of rent and salaries covers a facility that can produce, say, 1,000 units a month. At 800 units (the 200% scenario), you're within capacity and the formula holds. At 1,200 units, you'd need a second shift, a larger facility, or more equipment — and fixed costs jump to a new plateau. The break-even formula doesn't model that jump; it assumes you stay within the relevant range.

This is why break-even is a short-run tool, not a strategic plan. It tells you whether your current cost structure is viable at your current capacity. It doesn't tell you what to do when demand exceeds capacity — that's a capacity-expansion decision, and the new capacity comes with new fixed costs that shift the break-even point. The tool's four scenarios stay within the relevant range by capping at 200% of break-even; beyond that, the linear model breaks.

Gotchas

• Use contribution margin, not gross margin. Gross margin includes fixed manufacturing overhead in COGS, so FC / grossMarginPerUnit double-counts fixed costs. Use price − variable cost as the denominator. Variable cost = materials, direct labor, shipping, commissions — costs that scale with units. Fixed cost = rent, salaries, insurance — costs that don't.
• Price below variable cost means no break-even. If P ≤ VC, the contribution margin is zero or negative. More volume makes the loss bigger, not smaller. The tool shows a yellow warning; don't ignore it. Fix the pricing or the cost structure, not the volume.
• The 50% scenario is always a loss of half your fixed costs. Not approximately — exactly. At 50% of break-even units, profit = -0.5 × FC. The tool shows this for any input; it's a mathematical identity of the linear CVP model.
• Fixed costs are only fixed within a relevant range. The formula assumes fixed costs don't change with output. Past a capacity ceiling (a second shift, a bigger facility), fixed costs jump. The tool doesn't model that — use it within your current capacity, not for expansion planning.
• The contribution margin ratio is for revenue-based thinking. If you think in units, use FC / contributionMarginPerUnit. If you think in revenue (service businesses, multi-product averages), use FC / contributionMarginRatio. Both give the same break-even point in different units.
• Multi-product break-even needs a weighted average. The tool handles one product. If you sell three products with different margins, you need a sales-mix-weighted average contribution margin. The tool doesn't do this — compute the weighted average by hand, then divide FC by it.
• The CSV export is per-scenario, not continuous. The tool exports four rows (50/100/150/200% of BE), not a unit-by-unit table. If you need a sensitivity analysis at every unit count from 0 to 1000, build it in a spreadsheet with the same formula.
• Round units up, not to the nearest integer. If break-even is 400.3 units, you need 401 units to actually break even — 400 leaves you $7.50 short. The tool shows two decimal places (fmtUnits); don't round down when ordering or forecasting.
• The relatedTools link to "Profit Margin Calculator" is wrong in the tool UI. It points to /calculator-tools/roi (the ROI calculator), not a separate profit-margin tool. The ROI calculator is the right sibling for this guide's relatedTools.

Summary

• Break-even is one division. Break-even units = fixed costs ÷ (price − variable cost per unit). The denominator is the contribution margin per unit — the amount each unit contributes to covering fixed costs. Break-even revenue = break-even units × price. The tool computes both from three inputs.
• Contribution margin, not gross margin. Gross margin includes fixed overhead in COGS; contribution margin excludes fixed costs entirely. Plugging gross margin into the break-even formula double-counts fixed costs. Use variable costs (materials, direct labor, shipping) as the denominator, not COGS.
• Price below variable cost has no break-even. If P ≤ VC, each unit loses money before fixed costs are considered. The tool flags this with a warning. The fix is price, cost, or product — never volume. "Make it up on volume" is a trap.
• The 50% scenario is always a loss of 0.5 × FC. Profit is linear above break-even: 50% of BE = -0.5 FC, 100% = 0, 150% = +0.5 FC, 200% = +FC. The slope is the contribution margin per unit. The tool renders all four scenarios from the same three inputs.
• Fixed costs are only fixed within a relevant range. The formula assumes your current capacity. Past a capacity ceiling, fixed costs jump and break-even shifts. Use the tool for short-run decisions within current capacity, not for expansion planning.
• The contribution margin ratio is the revenue-side equivalent. CM / P × 100 gives the percentage of each revenue dollar that contributes to fixed costs. Break-even revenue = FC ÷ CM ratio. Use it for service businesses or multi-product averages where "units" is ambiguous.
• Calculate at the Break-Even Calculator; for compounding on retained earnings use Compound Interest Calculator, for return on an investment use ROI Calculator, and for debt-service coverage use Loan Calculator.