Break-even is the point where total revenue equals total costs, fixed costs (rent, software subscriptions, insurance, anything paid regardless of volume) plus variable costs (materials, per-unit labor, anything that scales with each sale).
The calculator divides fixed costs by the contribution margin per unit (price minus variable cost per unit) to find the number of units, or the revenue, needed before a business stops losing money and starts making it.
A small studio has $2,400/month in fixed costs (rent, software, insurance) and sells a service package for $150 with $30 in variable cost per package (materials, contractor time). Contribution margin is $120 per package.
Break-even: $2,400 ÷ $120 = 20 packages a month, or $3,000 in monthly revenue. Every package beyond the 20th contributes $120 of pure profit, which is why pushing volume even slightly past break-even matters more than it looks.
Fixed costs stay roughly the same regardless of how much you sell (rent, subscriptions, insurance); variable costs scale with each sale (materials, contractor fees, shipping). Getting this split right is the most common source of a wrong break-even number.
It's a floor, not a goal: knowing the exact volume where you stop losing money makes it obvious how much cushion (or risk) exists in a slow month, and how sensitive the business is to a price or cost change.
Any time a fixed cost changes materially (new software subscription, rent increase, added contractor), since break-even shifts immediately with fixed costs even if pricing stays the same.