Follow the cash balance through time
Let C₀ be initial available cash, R monthly cash receipts, and E monthly cash expenses. Constant monthly net burn is B = E − R. The scenario balance after m months is Cₘ = C₀ − mB. When B is positive, fractional depletion time is C₀/B months. When B is zero or negative, the model does not produce a finite cash-depletion date under unchanged assumptions. The displayed horizon is limited to 1,200 months. For a minimum reserve K below current cash, time to that threshold is (C₀ − K)/B when burn is positive; cash already at or below reserve has zero buffer time.
A revenue change with a visible effect
With 90,000 of cash, monthly receipts of 5,000, and expenses of 20,000, net burn is 15,000 and runway is six months. After three months, the constant-flow balance is 45,000. If receipts instead rise to 8,000 from the outset, burn becomes 12,000 and runway becomes 7.5 months. The example changes one constant assumption; it does not claim that future revenue will actually grow.
Cash timing can matter before month end
A fractional month assumes cash use is smooth enough to interpolate, while payroll, tax, and supplier bills may arrive in large steps. Receivables are not cash until collected, and reserved or pledged funds may not be available for operations. This basic model excludes changing exchange rates, treasury asset returns, new financing, and one-off liabilities. Reconcile those separately before relying on a balance path. Extending a scenario horizon does not create additional financing or make a cash-flow assumption more certain. Negative balances in the displayed path identify financing gaps and are not spendable funds.