Runway and raise timing calculator.
Runway is the number of months until cash runs out, and with a burn that grows each month it is shorter than cash divided by burn. With $2 million in the bank, a $90,000 monthly burn growing 2% a month, a six-month raise and a three-month cushion, runway is about 18.6 months and the raise should start by month 9.6.
Runway with rising burn
18.6 months
- Runway if burn stayed flat
- 22.2 months
- Latest month to start raising
- 9.6 months
- Monthly burn in the last month of cash
- $128,542
Indicative result from the numbers you enter. Not financial, tax or legal advice.
How it is calculated.
- Flat runway = cash / current monthly burn.
- With burn growing g per month, burn in month k = burn x (1 + g)^(k - 1). Cash runs out at m months where burn x ((1 + g)^m - 1) / g = cash, so m = ln(1 + cash x g / burn) / ln(1 + g).
- Latest month to start raising = runway - months a raise takes - cushion, never below zero (zero means start now).
- Burn in the last month = burn x (1 + g)^(months of runway rounded up - 1).
Worked example.
$2M cash, $90K burn growing 2% a month
| Step | Working |
|---|---|
| Flat runway | $2,000,000 / $90,000 = 22.2 months |
| Runway with rising burn | ln(1 + 2,000,000 x 0.02 / 90,000) / ln(1.02) = ln(1.444) / ln(1.02) = 18.6 months |
| Latest start | 18.57 - 6 - 3 = 9.6 months from now |
| Burn in the last month | $90,000 x 1.02^18 = about $128,500 |
Why rising burn matters.
Most founders quote runway as cash divided by this month’s burn. That number is only true if spending never grows. Once you hire against the plan, each month costs more than the last, and in the example a 2% monthly rise cuts more than three and a half months off the flat figure.
How much time to leave.
Raises often take longer than planned. A common piece of advice is to start a round with at least six to nine months of cash left, and to raise enough to give 18 to 24 months of runway after close. Treat those as starting points; a hot market moves faster and a slow one slower.
The cushion input is the cash you want left the day the money lands. With nothing left, any slip in the close becomes an emergency and weakens your hand on terms.
Prepare before the start date.
The latest start date is when investor meetings begin, not when you start getting ready. Update the model, refresh the metrics pack and bring the data room current in the month or two before it, so diligence does not eat into the raise.
Common mistakes.
- Using gross burn and ignoring customer receipts, or using net burn from a month with a one-off payment.
- Counting expected revenue as cash before it is collected.
- Planning the start date with no cushion, so a two-month slip leaves the company out of cash.
- Forgetting annual costs such as insurance, audits and software renewals that land in one month.