How to build a financial model for a small business

A good model isn't a wall of numbers — it's a small set of assumptions that flow through your profit, your cash, and your balance sheet so you can see what actually happens if a plan plays out.

What a financial model really is

A financial model is a spreadsheet that turns a handful of assumptions — how fast revenue grows, your margins, who you hire, what you spend — into a forecast of your three core financial statements.

The 'three-statement' standard is the professional bar: an income statement (profit), a cash flow statement (cash in and out), and a balance sheet (what you own and owe). The key is that they're linked, so changing one assumption ripples through all three.

Step 1: Separate assumptions from calculations

Every good model keeps its inputs in one place. Put your drivers — starting cash, revenue, growth, margins, headcount, expenses, loan terms, tax rate — on a dedicated assumptions tab.

A common convention colors input cells blue and formula cells black, so anyone opening the file knows exactly which cells are safe to change.

Step 2: Build the income statement

Start with revenue, subtract the cost of goods sold to get gross profit, then subtract operating costs like payroll and overhead to reach operating profit. Take out depreciation, interest, and tax to land on net income.

This tells you whether the business is profitable on paper — but profit is not cash, which is why the next statement matters just as much.

Step 3: Build the cash flow, then the balance sheet

Cash flow starts from net income and adjusts for non-cash items (like depreciation), changes in working capital (money tied up in receivables and payables), investment (equipment you buy), and financing (loans in, repayments out). The result is your true ending cash each month.

The balance sheet then ties it all together: cash and other assets on one side, debt and equity on the other. In a correct model the two sides always balance — a built-in check that your logic is sound.

Step 4: Read it for decisions, not decoration

The point of the model is the questions it answers: When do we run out of cash? What does hiring one more person do to runway? Can we afford this loan?

If you'd rather not build all of this from scratch, the free runway calculator below gives you the single most important answer — how many months of cash you have — and the full model does the rest.

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