Startup Runway: How to Calculate How Long Your Business Can Survive

The Core Runway & Burn Formulas

Calculating startup runway requires strict accounting discipline. The fundamental formulas are:

A Realistic Worked Example

Let’s evaluate a seed-stage startup with $180,000 in the bank:

• Monthly Salaries (Founder + 2 Engineers): $12,000
• Cloud Infrastructure (AWS + DBs): $800
• Software Subscriptions (GitHub, Slack, Notion, Stripe): $600
• Paid Customer Acquisition Experiments: $1,500
• Accounting & Legal Reserve: $500
• Total Gross Burn: $15,400 / month
• Monthly Cash Revenue Collected: $2,400 / month
• Net Monthly Burn: $15,400 - $2,400 = $13,000 / month
• Current Runway: $180,000 / $13,000 = 13.8 Months

Why Static Runway Calculations Fail

Static calculations assume expenses remain constant. In reality, expenses grow as user traffic expands (server bills, transaction fees) and unexpected annual tax filings or legal renewals occur.

The Three-Scenario Runway Model (Base, Bull, Bear)

Every founder should maintain a 3-tab financial model:

1. Bear Case (Default Dead): Zero revenue growth for 6 months. How many months until cash zero?
2. Base Case (Realistic): Modest 10% month-over-month revenue growth with controlled costs.
3. Bull Case (Optimistic): Rapid product adoption requiring hiring expansion.

Actionable Levers to Extend Runway Immediately

• Audit SaaS tools quarterly and eliminate unused seats.
• Incentivize annual customer prepayments with discounts.
• Shift specialized work to flexible project contributors rather than expanding full-time payroll prematurely.