A cash flow statement tracks the actual cash moving in and out of a company over a period of time, broken into operating, investing, and financing activities, separate from the profit or loss shown on the income statement.
A company can show a profit on its income statement and still run out of cash, most commonly when revenue is booked on an accrual basis before the customer actually pays, or when a large chunk of cash goes toward paying down debt or buying equipment, neither of which shows up as an expense on the P&L.
This is the statement that connects most directly to burn rate and runway: net cash used in operations, adjusted for financing and investing activity, is what actually determines how many months a company has left. A healthy income statement doesn't guarantee a healthy cash position, which is exactly why both get read together.
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