How Break-Even Units Calculator works

1. Scope

The Break-Even Units Calculator finds three numbers: the unit volume required to cover total fixed costs, the revenue at that volume, and the unit volume required to earn a target profit. It uses the classic contribution-margin formulation from managerial accounting. It is a single-product model — multi-SKU break-even requires a weighted contribution margin the tool does not compute automatically.

2. Inputs and outputs

Inputs: price per unit, variable cost per unit, total fixed cost (per period), optional target profit. Outputs: contribution margin per unit (price − variable), break-even units, break-even revenue, target-profit units, and the period's implied profit at a user-entered volume.

Engine source: src/lib/break-even/engine.ts.

3. Formula / scoring logic

contribution_margin_per_unit = price - variable_cost
contribution_margin_ratio    = contribution_margin_per_unit / price

break_even_units    = fixed_cost / contribution_margin_per_unit
break_even_revenue  = fixed_cost / contribution_margin_ratio
target_units        = (fixed_cost + target_profit) / contribution_margin_per_unit

4. Assumptions

• Fixed-vs-variable cost split is the user's responsibility. Rent, salaries, and subscription tools are fixed. Materials, payment-processing fees, shipping, and packaging are typically variable. Semi-variable costs (utilities, some payroll) need to be split manually.
• Linear variable cost. Each additional unit adds the same variable cost. Economies of scale, step-change tooling costs, and bulk-discount thresholds are not modelled.
• Single product / single contribution margin. For a multi-SKU business, compute a sales-mix-weighted average contribution margin before entering it. The tool does not do this for you.
• Revenue is recognised at sale. Subscription break-even needs to be computed on contribution-margin-per-month rather than per-unit — still works, but treat "units" as "customer-months".
• Contribution margin must be positive. If variable cost exceeds price, every unit loses money and break-even is undefined. The tool surfaces this explicitly.

5. Data sources

The contribution-margin formulation is standard in managerial-accounting curricula. The canonical reference:

• Garrison, Noreen, Brewer — Managerial Accounting, McGraw-Hill (any recent edition). Cost-Volume-Profit chapter.
• US Small Business Administration — break-even analysis (plain-English reference).

6. Known limitations

• Point estimate, no uncertainty. A ±10% swing in variable cost moves break-even by roughly ±10% in the opposite direction. The tool does not surface sensitivity bands.
• No time dimension. Break-even in units is meaningful; break-even in months requires knowing your sales rate.
• Multi-product averaging is manual. A coffee shop selling espresso and pastries needs a blended contribution margin weighted by the sales mix.
• No tax or financing costs. Break-even in this formulation is operating break-even, not post-tax.

7. Reproducibility

8. Change log

• 2026-04-24methodology page first published.