runway-calculator

Runway Calculator Skill

For any company spending more than it makes, one number governs everything: how many months of cash

are left. This skill computes net burn, runway, and the zero-cash date from your cash and P&L, judges

whether you're default alive or dead (Paul Graham's test — would you reach profitability on current

cash at current growth?), and shows the raise-or-cut needed to hit a target runway.

Required Inputs

Ask for these only if they aren't already provided:

• Cash in bank (today).
• Monthly revenue and monthly expenses (or net monthly burn directly).
• Monthly growth rate of revenue, if you want the default-alive check.
• Target — a runway you want to reach (e.g. 18 months) or a raise you're considering.

Output Format

Runway: [company]

1. The numbers (computed via the helper):

| Metric | Value |

|---|---|

| Net monthly burn | |

| Cash in bank | |

| Runway (months) | |

| Zero-cash date | |

| Default alive? | yes / no |

2. Default alive or dead — on current cash and growth, do you reach profitability before the cash runs out? State it plainly; it's the question investors ask first.

3. To extend it — the concrete moves and their effect: cut $X/mo → +Y months; raise $Z → +W months; or the growth rate needed to turn default-alive. Show the trade-off.

4. Caveats — flag if burn is rising (these numbers assume flat burn), and the buffer to keep (don't plan to zero — most raises take months).

Programmatic Helper

scripts/runway.py (stdlib only) computes runway and the zero-cash date:

# in.json: {"cash": 600000, "monthly_revenue": 40000, "monthly_expenses": 110000, "revenue_growth": 0.08}
python3 scripts/runway.py in.json
python3 scripts/runway.py in.json --json

Quality Checks

• [ ] Net burn = expenses − revenue (not gross spend) — and the zero-cash date is an actual date
• [ ] The default-alive/dead question is answered explicitly
• [ ] "To extend it" gives concrete cut/raise/growth options with their month impact
• [ ] Flags that the figures assume flat burn if burn is actually growing
• [ ] Recommends a cash buffer rather than planning to literally zero

Anti-Patterns

• [ ] Do not report runway off gross spend — net burn (after revenue) is the real number
• [ ] Do not assume flat burn silently — if headcount/spend is rising, say the runway is optimistic
• [ ] Do not plan to zero cash — a raise takes 3–6 months; runway should be measured to "must-raise-by," not "broke"
• [ ] Do not ignore growth — a fast-growing company can be default alive even while burning
• [ ] Do not present one scenario — show the cut-vs-raise-vs-grow trade-off

Based On

Startup cash-management practice — net burn, runway, and "Default Alive or Dead" (Paul Graham, Y Combinator).