Runway Calculator

Net burn — total cash out minus total cash in — is what actually shrinks the bank account, so it is the right divisor for runway. Gross burn (spending alone, ignoring revenue) is still worth knowing: it is your runway in the worst case where revenue goes to zero, which is the stress test lenders and investors run.

Six months of net burn is a sensible floor for a store, because e-commerce cash flow is lumpy: inventory is paid for months before it sells, and Q4 stock is bought in Q3. Businesses raising outside capital typically target 12–18 months, since fundraising itself consumes three to six of them.

Use a trailing three-month average of net burn rather than last month alone, which one inventory purchase or annual software bill can distort badly. If you are deliberately scaling spend, use your planned forward burn instead — runway based on yesterday’s smaller burn flatters you exactly when accuracy matters most.

If cash in exceeds cash out, net burn is negative and runway is effectively infinite — this calculator will tell you so rather than print a misleading number. The figure still worth watching is your worst-case runway: cash on hand divided by gross monthly spending, which is how long you survive if revenue stopped tomorrow.