What Is Runway?
Direct answerRunway is the number of months a startup can continue operating before it runs out of cash, based on how much cash it has and how quickly it is spending that cash.
The basic calculation is simple: divide your current cash balance by your monthly net burn. Net burn is the amount of cash the startup loses each month after accounting for cash coming in from revenue. For example, if your startup has $600,000 in cash and is losing $50,000 per month, it has about 12 months of runway.
Runway matters because it tells founders how much time they have to operate, reach important milestones, and decide when additional funding may be needed. Raising a round, including a SAFE round, increases your cash balance once the investment funds are actually received. New hires, higher expenses, or lower revenue increase your burn and shorten the runway.
How much time is left?
Think of runway as a countdown based on the cash your startup has today and how quickly that cash is being used.
Imagine your startup has $300,000 in the bank and loses $25,000 per month. At that pace, you have about 12 months of runway.
If you hire two more employees and your monthly net burn increases to $35,000, your runway drops to about 8.6 months. The amount of cash did not change, but the speed at which you are using it did.
The same works in the other direction. If your startup raises $500,000 and receives the money into its bank account, the cash balance increases. If your spending stays roughly the same, the additional cash gives you more time to operate.
This is why runway and burn rate are closely connected, but they are not the same thing.
Burn rate tells you how quickly cash is being used.
Runway tells you how long that cash is expected to last.
For a startup with revenue, founders often use net burn when calculating runway. Net burn accounts for both cash going out and cash coming in. If your startup spends $80,000 per month and receives $20,000 in revenue, its monthly net burn is $60,000.
The formula is:
Runway = Cash Balance ÷ Monthly Net Burn
So if you have $600,000 in cash and a $60,000 monthly net burn, your runway is 10 months.
The calculation is straightforward, but the number needs to reflect the startup's actual financial situation. A planned hire, a change in revenue, or a new expense can change the runway quickly.
What the SEC says, and what founders are actually asking
The SEC explains runway in its guidance on deciding how much capital a company needs to raise. It describes runway as the amount of time a company can survive at its current cash burn rate without raising additional capital, based on projected expenses.
Runway is not simply a number you calculate once and forget about.
The SEC connects runway directly to fundraising needs. Knowing how much time your current cash is expected to cover helps you think about how much money you need to raise and how long that new capital should support the business.
That means your runway calculation should reflect more than the cash sitting in your bank account today. Your expected expenses, hiring plans, revenue, and other changes to the business all affect how long that cash will last.
If your startup is planning to raise money, runway gives you a practical way to connect your current cash position to your next fundraising decision.
In a founder discussion about calculating runway and burn rate, one explanation described burn rate as how much cash a startup loses each month and runway as the amount of time that cash is expected to last.
The confusion makes sense because the two numbers are directly connected.
Burn rate is the speed at which the startup is using cash. Runway is the amount of time that cash is expected to last at that rate.
If your burn increases, your runway gets shorter. If your cash balance increases while your burn stays the same, your runway gets longer.
Founders also need to remember that runway is based on assumptions. If a startup expects to hire five people, increase marketing spend, or grow revenue, those changes need to be reflected in the calculation.
The practical goal is not simply to know the number. It is to keep the cash position, spending, fundraising activity, and milestones organized so the founder always knows where the business stands.
Runway is the amount of time your startup has before its current cash is expected to run out at its current net burn rate.
The basic calculation is cash balance divided by monthly net burn. Raising money increases runway by adding cash once the funds are received, while higher spending or lower revenue reduces it.
For founders, runway is most useful when it stays connected to the rest of the fundraising process. Your cash position, closed investments, fundraising milestones, documents, and deadlines all affect the decisions you make about the next round.
Cairnul keeps those fundraising records connected so founders have a clearer view of what has been raised, what has been completed, and what still needs to happen as the round progresses.
From cash raised to organized fundraising
Runway depends partly on knowing how much money has actually entered the business.
When a SAFE closes and the investment funds are received, that cash becomes part of the company's available cash. As more investors close, each investment adds to the overall amount raised during the round.
Cairnul tracks the fundraising activity and the cash added by closed SAFEs alongside the documents, investors, agreements, and milestones connected to the round.
That gives founders one place to keep track of what has been raised and which fundraising activity is complete instead of rebuilding the same information across spreadsheets, folders, and email threads.
Cairnul does not calculate your runway or provide financial advice. It keeps the fundraising information surrounding your round organized so the founder has a clearer record of what has happened as the company moves through the fundraising process.
Many founders treat runway as a fixed number.
It is not.
Your runway changes whenever the underlying numbers change. A new hire increases expenses. A new customer can increase revenue. A closed investment increases cash. A slower sales month can reduce cash coming in.
Another common misconception is that runway and burn rate are interchangeable.
They are not.
Burn rate tells you how quickly the company is using cash. Runway tells you how long the available cash is expected to last at that rate.
Founders also sometimes calculate runway using only the cash already in the bank while mentally including money they expect to raise soon. Those are two different things. Money that has not been received should not be treated as cash already available to the business.
The same applies to a fundraising commitment that has not yet closed. Until the investment funds are actually received, it has not increased the company's cash balance.
The practical takeaway is simple: calculate runway from the cash you actually have, use realistic burn assumptions, and update the number as your financial s
Get a clear view of your runway
Check your company's current cash balance.
Calculate your average monthly net burn using cash actually going out and coming in.
Divide your current cash balance by your monthly net burn to estimate your runway.
Review upcoming hires, contracts, and other planned expenses that could change your burn.
Separate cash already received from fundraising commitments or investments that have not closed yet.
Keep your fundraising activity, closed investments, documents, and milestones organized so your cash position is easier to track as the round progresses.
Frequently asked questions
Startup runway is the number of months a company is expected to continue operating before it runs out of cash at its current burn rate.
Divide your current cash balance by your monthly net burn.
For example, $600,000 in cash divided by $50,000 in monthly net burn gives you 12 months of runway.
Burn rate measures how quickly a startup uses cash. Runway measures how long that cash is expected to last.
Usually, yes. Once new investment funds are received, the company's cash balance increases. If the burn rate stays the same, the additional cash extends the runway.
Usually, yes. A new hire increases the company's expenses. If that increases monthly net burn, the startup's runway becomes shorter unless the additional spending is offset by additional revenue or capital.
There is no universal number that works for every startup. The right amount depends on the company's stage, spending, revenue, business model, and the milestones it needs to reach before it needs additional capital.
Keep your fundraising cash and records connected
Cairnul helps founders organize investors, documents, and compliance in one place, so the whole raise stays clear from first sale to close. Join the waitlist to be among the first founders to run a cleaner, more organized round.
Join the waitlistDisclaimer. This content is provided for educational purposes only and does not constitute legal, tax, or investment advice. Fundraising rules, filing requirements, and fees may vary by jurisdiction and change over time. Always confirm current requirements with qualified counsel or the relevant regulator.