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Runway Calculator

Enter Cash on hand, Monthly net burn and Monthly burn growth — every figure updates as you type. Nothing you type leaves your browser.

How do you calculate Runway?

Runway is how many months of cash a company has left at its current net burn. This calculator compounds burn growth rather than assuming a flat cost base, because a company still adding headcount runs out of money materially sooner than cash divided by today's burn suggests. When net burn is zero or negative the result is zero months, which here means runway is unbounded rather than exhausted.

Runway

16.5

Months until cash reaches zero, with burn growth compounded. 0 means unbounded when net burn is at or below zero.

Runway if burn stayed flat: 21The naive cash ÷ burn figure. Almost always the more optimistic of the two.
Months lost to burn growth: 4.5The gap between the two figures — the cost of a compounding cost base.

Results are rounded for display; the calculation runs at full precision.

The maths

How Runway is calculated

The formula this calculator runs, written out so you can check it against your own model rather than trust a black box.

Runway = ln(1 + (Cash × g) ÷ Net burn) ÷ ln(1 + g) · with g = 0 this reduces to Cash ÷ Net burn

Cash: Cash you could draw on today, including short-term deposits. Exclude committed but unreceived investment, and exclude any facility you have not actually drawn.
Net burn: Monthly cash consumed after customer receipts — gross spend less collections. Gross burn produces a runway figure that is wrong by the entire size of your revenue.
g: Monthly burn growth as a decimal. Enter 3 for 3% and the calculator converts it. Zero holds the cost base flat; a negative value models a planned reduction.

Reading the result

What the number is telling you

Bands are directional, not verdicts. Stage, price point and contract length move every one of them, so treat these as a starting point for the conversation rather than a grade.

Under 6 months: Acute. This is shorter than a fundraising process typically takes, so the realistic options narrow to bridge financing from existing investors or an immediate reduction in burn. Both take time to arrange, which is the argument for acting at the top of this band rather than the bottom.
6–12 months: A raise should already be underway. Starting a process with nine or ten months of runway leaves room for a slow first term sheet, a failed conversation and the weeks between signing and money arriving. Companies that begin at six months are negotiating from a position everyone in the room can see.
12–18 months: Working room — the standard position immediately after a round. Enough time to hit a milestone that changes the next conversation, provided the milestone is chosen now rather than discovered later. Recheck this figure whenever headcount plans change, since burn growth compounds quietly.
Over 18 months: Comfortable, and worth a second question: whether burn is too conservative for the opportunity in front of you. Long runway with slow growth is capital sitting idle. If unit economics are sound, deliberately shortening runway to fund acquisition is often the better trade.
0 months with net burn at or below zero: Runway is unbounded — the business is not consuming cash, so there is no date at which the balance runs out. The calculator has no finite number to show. Runway has stopped being the constraint, and the planning question becomes how much burn to take on deliberately.

Flat runway is optimistic by construction

Cash divided by burn is the figure almost everyone quotes, and it silently assumes the cost base you have today is the cost base you will have in eighteen months. For a company that is still hiring, that assumption is false in a direction that always favours the optimist.

At the defaults above, a cost base growing 3% a month — roughly one additional hire per quarter for a small team — costs about four and a half months of runway against the flat calculation. That gap is usually larger than the margin by which fundraising timelines slip, which is why the flat number is a poor basis for deciding when to start a raise.

Zero months means one of two things

This calculator returns zero when net burn is at or below zero. That does not mean you are out of cash — it means the opposite. A company whose collections cover its spending is not consuming its balance, so there is no month at which the balance reaches zero and runway is effectively unbounded. There is no finite number to display, so zero stands in for it.

Zero also appears when cash on hand is zero, where it means exactly what it says. The two cases are trivial to tell apart by looking at the net burn input beside the result: negative or zero burn is the unbounded case, positive burn with no cash is the literal one. If you are in the first case, the more useful exercise is deciding how much burn you could deliberately take on — a business that is default alive can choose to spend into growth, and burn rate is where that plan starts.

What to do with the number

Runway is a planning input, not a score. Three adjustments make it more honest:

Subtract the raise. A funding process takes months from first meeting to money in the bank, and it consumes founder time that would otherwise go to the business. Runway that ends when the money runs out is runway that ended some time ago.
Model the cut, before you need it. Knowing what runway looks like at a reduced cost base converts a crisis into a decision. Run this calculator a second time with the burn you would have after the reduction.
Do not count committed-but-unreceived funding. Term sheets fail, tranches are milestone-gated, and a signed commitment is not a bank balance.

The other half of the picture is what your burn is buying. If it is funding acquisition rather than fixed cost, payback period tells you how fast that spend returns, and LTV:CAC tells you whether it should be spent at all. Bastle's forecasting runs the same arithmetic against live billing data, so the revenue side of net burn updates as your subscriptions actually move.

Definition

Where Runway gets argued about

A calculator settles the arithmetic, not the definition — and the definition is where most disagreements about this number actually live. The glossary entry covers the conventions, the edge cases and how Bastle handles each one.

Read the Runway definition Browse the metric glossary

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Frequently asked questions

Should runway use gross burn or net burn?

Net burn — gross spend less the cash actually collected from customers. Gross burn ignores revenue entirely and therefore understates runway by the full size of your collections, which for a company at any scale makes the figure meaningless. The one place gross burn belongs is a downside scenario where you model revenue falling away completely.

Why does the calculator show zero when we are profitable?

Because there is no finite answer to display. If net burn is zero or negative, the cash balance is not falling, so there is no month at which it reaches zero and runway is effectively unbounded. Zero is the placeholder for that. It also appears when cash on hand is zero, where it means exactly what it says — check the net burn figure beside the result to tell the two apart.

Should I model burn growth or keep it flat?

Model it if you are still hiring, which most funded companies are. Flat runway assumes today's cost base persists unchanged, and even modest compounding — 2 to 3% a month, roughly a hire a quarter for a small team — removes several months from the answer. Keep it flat only when headcount and spend are genuinely frozen, and use a negative value to model a planned reduction.

How much runway should I have before starting a raise?

Enough that the process finishing late is inconvenient rather than fatal. Raising typically takes several months from first meeting to funds received, and it absorbs a large share of founder attention while it runs, so runway that ends the week the money would arrive is already too short. Twelve months at the start of a process is a common target; nine is workable; six leaves the other side of the table with all the leverage.

Does committed funding count toward runway?

Not in the headline figure. Term sheets fall through, tranches are gated on milestones, and undrawn debt facilities carry conditions. Runway should reflect cash you could spend today. Model the committed money as a separate scenario alongside the base case, so the plan is legible whether or not it arrives.

How often should runway be recalculated?

Monthly, and immediately after any change to headcount, pricing or a large contract. Runway is the metric most likely to be checked once after a round and then quietly assumed for a year, which is exactly how a compounding cost base does its damage. Because it depends on net burn, it also moves whenever revenue moves — a churn event shortens runway as surely as a hire does.

Stop recalculating Runway by hand.

Connect Stripe and Bastle keeps Runway current — backfilled to your first customer, segmentable, and traceable to the invoices behind it. Free while in beta, no card required.

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