Free tool
How long the money lasts
Runway is how many months your cash lasts at the current net burn. This calculates it from cash, monthly costs, and revenue, then shows what adding a hire or a marketing budget does to that date. The second number is the one that changes hiring decisions.
Last reviewed 27 August 2026
Result
Runway today
16 months
Net burn $45,000 a month before growth
Runway with $12,000 a month added
10 months
Costs you 6 months of runway
This leaves enough runway to see whether the spend worked before you need to raise, which is the condition that makes the decision reversible.
How this works
What the numbers mean.
- 01Runway is simulated month by month rather than by dividing cash by burn, because revenue growth compounds and a flat division ignores it.
- 02Revenue grows by your stated rate each month while costs stay flat. That is optimistic on costs and roughly right on revenue for a stable growth rate.
- 03The second figure adds your proposed new spend. The difference between the two is the real price of the decision, expressed in months rather than dollars.
Assumptions and limits
- Costs are held flat. In reality they rise with headcount, so treat the output as a ceiling.
- A constant growth rate is a simplification. Growth is lumpy, particularly below a hundred customers.
- This models cash, not covenants, receivable timing, or tax. Check with whoever does your books before acting on it.
Questions about this tool
How much runway should I keep?
The common rule is eighteen months after a raise and never below nine, because raising with under nine months left removes your ability to walk away from a bad term sheet. That is a negotiating position as much as a financial one.
Should marketing spend come out of runway?
It depends entirely on whether the channel has a measurable payback shorter than your remaining runway. Paid acquisition with a four-month payback is a different decision from content and community work that pays back over a year. The second needs runway you actually have.
Why does the model use compounding revenue?
Because dividing cash by monthly burn ignores that revenue grows while you spend, which understates runway for any growing company. The difference is small at low growth rates and very large above ten percent a month.
This tool is free and there is nothing to sign up for. If you would rather have the work done than calculate it, that is what Zway does.