Startup runway calculator math is one division, spendable cash on hand divided by monthly net burn, and the output is months of runway plus a zero-cash date. Net burn is the only correct denominator, since gross burn turns 15.0 months into 5.8 on the same balance sheet. Indinero has built runway forecasts for growth-stage companies since 2009, with bookkeeping, accounting, tax, and fractional CFO under one monthly engagement.