Gross margin is what is left of revenue after the direct cost of delivering what you sold. It is the money available to cover everything else — rent, salaries not tied to delivery, marketing, and profit.

The calculation

Revenue minus cost of goods sold, divided by revenue. Bill $10,000 for a project that costs $4,000 in contractor time to deliver and your gross margin is sixty percent.

The hard part is deciding what counts as a direct cost. Anything that scales with the work belongs there: contractors, delivery staff time, hosting for customer workloads, transaction fees, support attached to a specific account. Costs that exist whether or not you sell anything — rent, accounting, the website — sit below the line.

Service businesses often leave out the founder's delivery time, which makes the margin look like a product business. If you are delivering the work, your time is a direct cost, and counting it at zero hides the fact that the business has no margin at all once you stop.

Why it sets the ceiling

Gross margin decides what the business can afford to do. It funds acquisition, so it caps customer acquisition cost and drives lifetime value directly.

At thirty percent, every $1,000 of new revenue gives you $300 to run the company. At eighty percent it gives you $800. That difference decides whether you can afford a salesperson, how fast you can grow, and how long you survive a slow quarter.

It is also the clearest signal of what kind of business you own. High margin usually means leverage — the thing you sell costs little to deliver again. Low margin means you are reselling time, and growth requires proportionally more people. See leverage and productization.

Improving it

Three levers, in order of difficulty. Raise prices, which moves margin immediately and costs nothing. Reduce delivery cost, usually through process and scope control — see scope creep. Change what you sell, which is the largest move and the slowest.