State the assumptions beside the result
The simple calculation assumes a stable monthly pattern. If available cash is 120 units and net monthly cash outflow is 20 units, the arithmetic gives six months under that assumption. This is a numerical illustration, not a recommendation for a real business.
Check what the estimate leaves out
Payment timing, one-time costs, liabilities, seasonality, hiring, and changes in revenue or spending may change the result. When net outflow is zero or negative, the simple calculation does not give a meaningful finite runway. Use qualified financial support for actual cash planning decisions.