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Tool 01 / Business Numbers Lab

Could the numbers work?

Compare two possible months. See what each sale contributes, what volume covers fixed costs, and what remains after the costs you include.

Entrepreneurship Basics · Business Numbers Lab · entrepreneurshipbasics.com/tools/business-numbers/

No automatic saving. Save your work as a JSON file before you leave. Loading a valid file replaces the current entries.

Starts with a hypothetical service example. Change the inputs to explore your own assumptions. Both cases use one product or service and monthly figures.

Currency changes the label only.
No exchange-rate conversion.

Base month
Alternative month

Use non-negative amounts with at most two decimal places. Limits: price and variable cost 1,000,000; fixed costs 1,000,000,000; whole units 1,000,000. Keep one consistent currency and month.

The month, worked out.

Based only on your inputs

BASE MONTH

Simplified operating result / month

Revenue
Total variable costs
Fixed costs
Contribution per unit
Contribution margin
Break-even volume

ALTERNATIVE MONTH

Simplified operating result / month

Revenue
Total variable costs
Fixed costs
Contribution per unit
Contribution margin
Break-even volume

How the model works

Four inputs. Clear arithmetic.

  • Contribution per unit = price − variable cost per unit.
  • Revenue = price × units.
  • Simplified operating result = contribution × units − fixed costs.
  • Break-even units = fixed costs ÷ contribution, rounded up to a whole unit when contribution is positive.

A $100 price, $40 variable cost, and $1,200 fixed costs give $60 contribution and a 20-unit break-even target. At 30 units, the result is $600.

The SBA break-even calculator provides the standard formula. Our tool adds a side-by-side month comparison and local file backup.

What this cannot tell you

A model needs a reality check.

This is not cash flow, take-home pay, a tax calculation, or an accounting forecast. It excludes taxes, financing, depreciation, startup spending, and owner pay unless you explicitly include applicable operating costs in your inputs. It assumes constant unit price and cost, one product, and no capacity limit.

Include payment fees, delivery, refunds, support, and labor where relevant without counting a cost twice. The cost-classification example shows how to separate a mixed bill. A whole-unit break-even target may slightly exceed the exact mathematical threshold. With no positive contribution, selling more cannot create a positive result.

Check whether you can actually sell and deliver the target volume. The capacity worksheet budgets the hours, and the break-even limitations guide tests the model’s assumptions. Use the validation canvas to record the test. The employment comparison helps separate business sales from replacement income.

Source checked November 5, 2026. Educational calculations; no result is a prediction.