Runway Converts Net Burn into Time
Net burn measures how much cash decreases during a period after modeled inflows and outflows. Runway divides available cash by the recurring net burn rate when burn is positive, producing an estimate of how long current cash could last under unchanged conditions.
Runway is highly sensitive to hiring, revenue timing, financing, one-time purchases and collection delays. If cash flow becomes neutral or positive, a finite burn-based runway is no longer the appropriate interpretation.
Runway is a snapshot based on the current pattern of cash in and cash out. A growing company rarely keeps both revenue and expenses perfectly flat, so the result should be updated as hiring, sales, funding or large one-time costs change. Gross burn is useful for understanding operating spend; net burn is useful for understanding how quickly cash is actually declining after revenue. If net burn approaches zero or becomes negative because revenue exceeds cash expenses, a simple cash-divided-by-burn runway formula stops being meaningful.
Frequently Asked Questions
What if the business is cash-flow positive?
If modeled inflows equal or exceed outflows, cash is not being consumed at a positive net burn rate, so a finite runway from burn is not meaningful.
Why can runway change quickly?
Because both the available cash balance and monthly net burn can change with revenue, hiring, financing and one-time expenses.
Why should runway be recalculated regularly?
Because revenue, payroll, hiring, financing and one-time expenses change the monthly net cash outflow. A runway estimate based on last quarter's burn can quickly become stale.
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