The formula, without the mystery.
Break-even units = ceil(fixed costs / (price − variable cost))
A worked example
With 1,000 fixed costs and 30 contribution per sale, break-even is 34 units. Those units generate 1,700 revenue and 20 profit after costs.
Which costs belong in fixed costs?
Use costs that do not change with each sale during the selected period, such as rent or a flat software subscription. Put payment fees and fulfillment in variable cost.
Keep the assumptions consistent
Use one planning period and one currency. Enter amounts consistently excluding sales tax or VAT. These simplified models do not account for uncertainty, inventory limits, working capital or progressive taxes. Results are planning estimates.