About this calculator
Runway is the number of months your startup can operate before running out of cash. Runway = Cash / Net burn, where net burn = monthly expenses − monthly revenue. This calculator also models the impact of monthly revenue growth, projecting "default alive" — the month when revenue catches up to burn.
Why runway is the single most important startup metric
Cash-out kills more startups than any other single cause. Paul Graham’s 2015 essay "Default Alive or Default Dead" framed the question: at your current growth trajectory, will revenue cover burn before cash runs out? Default-alive companies can keep operating regardless of fundraising. Default-dead must raise — and bad fundraises (low valuation, bad terms) often destroy more value than they create.
When to fundraise
- 12–18 months runway — Start the next round’s conversations. You have time to walk away from bad terms.
- 6–12 months — Active fundraise. Closing inside this window is hard but doable.
- Under 6 months — Crisis. Cut to extend runway while raising. Founder takes salary haircut, freezes hiring.
- Under 3 months — Bridge financing from existing investors, often at unfavorable terms.
The default-alive math
If revenue grows 10% per month and net burn is $50k/month, revenue will catch up to monthly expenses in n months where revenue × 1.1n = expenses. The calculator simulates this month by month. Companies that look default-dead at 5% growth can be default-alive at 15% growth — small growth-rate changes have huge impact on the runway equation.
Cut burn or raise revenue?
Cutting burn is faster and within your control. Raising revenue is slower but compounds. Most successful startups do both during runway crises: trim 20–30% of burn while doubling down on the 1–2 growth experiments most likely to move revenue.
What this calculator doesn’t model
One-time expenses (legal for fundraising, severance), seasonality (most B2B SaaS has Q4 strength), accounts receivable (large customers pay 30–90 days late), or revenue churn shocks. Real-world runway is usually 1–2 months shorter than the model says because of timing friction.