Startup Runway: Calculate Burn and Plan for Cash Risk

Use cash, not accounting profit

Gross burn is a defined measure of cash outflows over a period. Net burn subtracts relevant cash inflows. Document exactly what is included: operating payments, financing, taxes, debt principal, and equipment spending can be treated differently in different reports.

For the simple model in this guide, net burn is recurring monthly cash outflow minus recurring monthly cash inflow, before new financing. Restricted cash and money that cannot be used for operations should not automatically count as available runway.

Simple runway = available cash ÷ positive monthly net burn

If net burn is zero or negative, this constant-burn formula does not produce a finite depletion date. That is not a guarantee of unlimited runway; a future expense or revenue decline can change the cash trajectory.

Worked example: the cash floor matters

Suppose a business has $480,000 of usable cash, spends $80,000 per month, and collects $40,000 per month. Its monthly net burn is $40,000.

The reserve is a management decision, not an automatic legal or accounting requirement. It can provide room for unavoidable commitments or a controlled change of plan. A “twelve-month runway” headline hides the earlier decision point if management cannot responsibly operate down to zero.

Build a monthly cash schedule

Start with opening cash. Add collections when they are expected to arrive, not when an invoice is issued. Subtract payroll, vendor payments, taxes, debt service, capital purchases, and other actual cash movements when due.

Ending cash = opening cash + cash inflows − cash outflows

Carry ending cash into the next month. For each forecast line, distinguish committed amounts from assumptions. A signed contract with delayed collection is not the same as an unsigned sales opportunity, and neither is the same as cash already received.

Annual software renewals, insurance premiums, bonuses, and inventory orders can produce large one-time drops. A trailing monthly average can miss these even when its historical calculation is correct.

Model decisions as scenarios

Create a base case, a lower-collections case, and a planned-spending case. Add hiring only from the expected start date, including recruiting fees, equipment, taxes, benefits, and any other relevant cost.

Avoid assuming every cost can be reduced instantly. Contracts, notice periods, severance obligations, and operational dependencies may delay savings. Seek appropriate professional advice for employment, financing, and contractual decisions rather than treating the cash model as permission to ignore obligations.

For a growth business, separate revenue recognition from collection timing. A profitable customer contract can increase near-term burn if delivery costs arrive before payment.

Set triggers before the cash becomes urgent

Choose the cash balance or forecast runway that triggers each action: freeze discretionary spending, change hiring plans, revisit pricing, seek financing, or reduce a project scope. The right trigger depends on the time required to execute the action and the uncertainty involved.

Treat prospective fundraising as a scenario until it is sufficiently certain to include in the base cash plan. A valuation discussion or positive investor meeting is not available cash.

A financing event may extend runway while adding repayment requirements, dilution, or restrictions. Those effects deserve their own decision analysis; the runway metric alone cannot rank the options.

Update the forecast with actuals

Reconcile the opening balance to the bank records and replace completed months with actual cash movements. Investigate large differences between planned and received collections and between planned and paid expenses.

Use the rolling forecast to improve decisions, not to defend an old number. When burn is changing quickly, a static “cash divided by last month's burn” estimate should be labeled as a snapshot, not a reliable exhaustion date.

Use this guide thoughtfully. Examples illustrate a calculation method, not a guaranteed outcome. The usefulness of any result depends on the definitions, measurements, and assumptions used.