Cash burn rate answers an uncomfortable but simple question: how fast is the bank balance melting away when outflows exceed inflows? Originally a startup metric that determines how long equity funding lasts, it matters for any company going through a growth phase, a revenue downturn, or an investment period with negative cash flow.
This guide walks through the gross and net formula, a fully worked example, the runway calculation — and when a normal fluctuation turns into a signal that demands a response. For the underlying cash flow concept itself, see cash flow basics.
Gross and net cash burn rate: the formula
Two variants of the metric are used in practice, and confusing the two is the most common mistake:
| Metric | Formula |
|---|---|
| Gross burn rate | monthly operating outflows (inflows not netted off) |
| Net burn rate | monthly outflows − monthly inflows |
| Runway | available cash ÷ monthly net burn rate |
Gross burn rate shows only the cost base — it answers how high monthly outflows are for payroll, rent, materials and other running costs. For the question of whether, and how fast, the cash balance is falling, only net burn rate matters, because it nets off inflows. A company with a high gross rate but equally high inflows can have a net burn rate close to zero — and conversely, a company with a low gross rate but collapsing inflows can still lose cash fast.
Net burn rate can also be derived directly from the balance: opening cash balance minus closing cash balance, divided by the number of months covered. Both routes arrive at the same result — as long as no one-off events, such as a capital raise, a loan drawdown, or a large capital expenditure, distort the balance in between. Where such events occur, strip them out of the calculation, or they will distort the ongoing picture.
A worked example
A company in an investment phase pays example monthly costs of €180,000 in running expenses (payroll, rent, materials) and records monthly cash inflows of €140,000. The cash balance at the start of the month is €900,000.
| Metric | Calculation | Result |
|---|---|---|
| Gross burn rate | monthly outflows | €180,000 |
| Net burn rate | €180,000 − €140,000 | €40,000 |
| Runway | €900,000 ÷ €40,000 | 22.5 months |
Read plainly (example values): if the trend continues unchanged, the cash balance shrinks by €40,000 a month, and the funds on hand last roughly 22.5 more months on paper. If inflows rise to €160,000, net burn rate falls to €20,000 and runway doubles to 45 months — the lever on the inflow side works disproportionately, because it moves the gap itself, not just one side of it.
Calculating runway: how long does the money last?
Runway is the real steering metric behind burn rate: it translates a euro figure per month into a span of time that is easier to plan against. Two figures feed into it — available cash and, where they exist, undrawn, firmly committed credit lines that could be drawn quickly if needed. How much of such a line is actually free is shown by a bank mirror; a rule of thumb for how large the overall buffer should be is covered in the guide on cash reserves.
The limits of the calculation matter. Runway is a projection based on the recent trend, not a guarantee. It assumes net burn rate and balance can be extrapolated in a straight line — an assumption that breaks down quickly in a seasonal business or ahead of a large incoming order. A single runway figure is therefore a rough orientation, not a substitute for a week-by-week forecast.
LiquidityLens derives net burn rate and the resulting low point directly from your real bank transactions, AI-powered — continuously, not only at month-end.
See the Liquidity Control SprintWhen does burn rate become a warning sign?
There is no fixed threshold, because the right net burn rate depends on the situation: during a planned investment phase with secured follow-on funding, a negative figure sustained for months is a deliberate, unremarkable choice. Two comparisons matter instead.
The first is checking runway against your own lead time: does it still leave enough time for a countermeasure — cutting costs, starting a bank conversation, negotiating a credit line — to take effect before the balance falls below your defined minimum reserve? That lead time differs for every company and depends on how quickly costs can actually be cut or new funding raised.
The second is your own trend over time: a net burn rate rising over several months while runway keeps falling at the same time is a more reliable signal than any single month’s figure — much like a rising DSO or a growing share of overdue receivables signals an approaching cash flow shortage long before the bank balance itself shows it.
Tracking it continuously, not once a month
Deriving burn rate from the month-end close has a structural downside: it shows what happened last month, not where the current week is heading. Tracking net burn rate week by week from actual inflows and outflows instead surfaces a deterioration weeks earlier — in exactly the form a 13-week cash flow forecast delivers, and the same discipline that underpins cash flow forecasting as a whole.
The free Excel template sets weekly inflows against outflows and flags automatically when the balance would fall below your minimum reserve — a starting point for watching burn rate continuously instead of once a month.
FAQ
The most common questions about cash burn rate are summarized at the end of this page.