Calculate net burn and runway
Returns net cash burn by month over the last six months and divides current cash by the average to estimate runway.
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You are a finance director calculating cash burn and runway.
Context: cash movements are in {cash_field} and the reporting date is {date_field}.
Current cash balance is {cash_balance}. Use the last six months.
{cash_data}
Task: compute monthly net burn and estimate runway.
Output format:
- Net burn for each of the last six months (cash out minus cash in; positive = burn).
- Average monthly net burn over the window.
- Runway in months = current cash balance / average monthly net burn.
- A note on whether burn is rising, falling, or steady, since that changes how
much to trust the average.
- Net burn is the net change in cash, not just expenses; exclude one-time
financing events from operating burn, or show with and without, and say which.
Run it in four steps
- Export six consecutive months of cash movements, with one-time financing and non-operating events identifiable.
- Paste it into
{cash_data}, point{cash_field}and{date_field}at the right columns, and enter your reconciled{cash_balance}. - Run it for monthly net burn, average burn, and runway.
- Use the trend note, not just the average; if burn is rising, the average overstates runway, so exclude the one-time events first.
When to reach for this prompt
Use this for any board update, investor check-in, or internal "how long do we have" moment. It is the canonical cash question, and the trend note is what keeps the runway figure from being naive, since a company with rising burn has a shorter runway than its average implies. It is not a substitute for a real forecast; a backward-looking average cannot see a known large payment next month, so use a 13-week cash forecast for anything forward-committed.
What you can expect back
Net cash burn, last 6 months
| Month | Cash in | Cash out | Net burn |
|---|---|---|---|
| Jan | 1,720K | 2,010K | 290K |
| Feb | 1,680K | 2,040K | 360K |
| Mar | 1,810K | 2,090K | 280K |
| Apr | 1,650K | 2,120K | 470K |
| May | 1,700K | 2,180K | 480K |
| Jun | 1,740K | 2,210K | 470K |
| Average monthly net burn | 392K |
Current cash balance: $6.8M
Runway: $6.8M / $392K = approximately 17 months on the trailing-six-month average.
Burn is rising; the most recent three months average about 473K, which puts runway closer to 14 months. The lower figure is the more prudent planning number, though actual runway will depend on future spending decisions.
This prompt has real limitations you should understand.
Runway is a single division, so the danger is not the arithmetic but the softness of its inputs. Net burn is the change in cash, which folds in collections timing, deferred revenue, and working-capital swings rather than just the P&L, so a month that "burned" $470K may have spent far less and simply collected late. The cash lens and the expense lens disagree, and runway uses cash.
One-time events distort the average in both directions. A financing inflow, a tax payment, or an annual insurance renewal lands in one month and skews average burn unless it is stripped out, which is why the prompt asks for an operating-only view. And a trailing average ignores trajectory: when burn is climbing, dividing cash by the six-month average overstates runway, which is precisely the error that leaves companies caught short, and the reason the trend note pushes toward the more conservative figure.
A runway number worth putting in front of a board needs cash movements separated into operating versus financing, with non-recurring items isolated and the burn trend made explicit rather than averaged away. That separation is a property of how cash data is categorized upstream, and it is what turns a single division into a figure leadership can plan against.
What your data needs to look like
- A cash-movement field (net change, or cash in and cash out) at monthly grain
- A reliable current cash balance
- One-time financing and non-operating events identifiable, so they can be excluded
- Six consecutive months of clean cash data
See how FinanceOS handles this prompt on real financial data.
Book a 20-minute walkthrough. We’ll run this exact prompt against a sample dataset reconciled through FinanceOS, and show you what changes when the data underneath is right.
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