How to Calculate Startup Runway and When to Raise

Startup runway is cash in the bank divided by monthly net burn, which is cash out minus cash in. With 1.8 million USD and a net burn of 150 thousand a month, runway is 12 months. Start raising while you still have nine to twelve months left.

That's the short answer, and it's a good first approximation. The longer answer matters because the simple formula assumes nothing changes: revenue stays flat, costs stay flat, nobody gets hired and no customer pays late. Real companies change every month, and the decisions you make in the next quarter can move your cash-out date by half a year in either direction. This guide covers the basic calculation, the better version, and how to use it to time a raise.

The basic runway formula

Runway in months equals current cash divided by monthly net burn.

• Current cash is money you can actually spend: operating bank accounts and liquid short-term holdings. Leave out anything restricted, such as collateral for a lease.
• Gross burn is everything you spend in a month: payroll, rent, software, marketing, contractors, everything.
• Net burn is gross burn minus cash coming in from customers. This is the number that drains the bank account.

Use cash numbers, not accounting numbers. An annual contract paid upfront is a big inflow in one month and nothing for the next eleven. Revenue recognition spreads it evenly, but your bank account doesn't. Most founders use an average of the last three months of net burn to smooth out lumpy months, and that's a sensible starting point.

In the example above, a company with 1.8 million USD in the bank, 120 thousand of monthly receipts and 270 thousand of monthly spending burns 150 thousand a month. Divide 1,800 by 150 and you get 12 months.

Why the simple formula is often wrong

The simple version treats burn as constant. It rarely is. Three things usually move it.

Revenue growth

If revenue grows, net burn shrinks every month, and runway is longer than the simple formula says. Take the same company and let receipts grow 5 percent a month while costs stay flat. Net burn falls from 144 thousand in the first month toward zero, the company reaches break-even around month 17, and the bank balance bottoms out at roughly 460 thousand. On paper, it never runs out of cash. That's a very different story from "12 months".

Hiring

Now add four hires starting in month three, at a fully loaded cost of 12 thousand each per month. Same growth, same everything else. The extra 48 thousand a month means the company runs out of cash in month 13. Those four hires turned "never runs out" into roughly a year of runway.

Of course, hires usually exist to produce something. Four sales reps should eventually add revenue, after they ramp. That's exactly why runway needs a model rather than a division: the answer depends on when costs start, when results arrive and how confident you are in the ramp. A proper headcount planning model captures salary, taxes, benefits, equipment and ramp time for each role.

Timing and one-offs

Annual software renewals, insurance, tax payments, a customer that pays 60 days late, a large prepaid contract: all of these create bumps that a monthly average flattens away. If one of those bumps lands in the month your cash is lowest, it matters. A weekly cash view for the next quarter catches those, and our guide to the 13-week cash flow forecast explains how to build one.

A better way to calculate runway

Instead of dividing, project. Build a month-by-month forecast of cash for the next 18 months or longer, with the main drivers.

1. Revenue from current customers, expected growth, churn and new sales, as cash receipts.
2. Payroll from the actual team plus planned hires with start dates and fully loaded cost.
3. Other costs by category, with known changes such as a new office or a marketing push.
4. One-off items such as annual renewals and tax payments in the right months.

Then read off four numbers: the month cash hits zero, the lowest cash balance, the break-even month if there is one, and how much cash you'd need to reach break-even or the next milestone with a safety buffer. Those four numbers are what investors, boards and lenders actually want to see.

A runway calculator does this projection from a handful of inputs: revenue, growth, costs, cash, planned hires and marketing changes. It's a quick way to see the shape of the curve before you build the full model.

Default alive or default dead

A useful framing popularized in startup circles asks one question: if nothing changes in your current growth and spending, do you reach profitability before the money runs out? If yes, you're default alive. If no, you're default dead, and you'll need either to raise, to cut, or to grow faster.

The answer comes straight from the projection above. In our example, the company without the new hires is default alive. With them, it's default dead unless the hires produce revenue fast enough. That's a much more useful conversation for a leadership team than a single runway number.

When to start raising

Common advice from investors and experienced founders is to start a fundraise with somewhere around nine to twelve months of runway left, sometimes more in a difficult market. The reasoning is simple arithmetic.

• Preparing materials and a target list takes several weeks.
• A round often takes three to six months from first meetings to money in the bank, and can take longer.
• You want a buffer of several months after closing, in case the process drags or the market turns.
• Raising with little runway left weakens your negotiating position, and investors can usually tell.

Work backwards from your projected cash-out date, not the simple-formula one. If the projection shows cash running out in month 13, you'd want to be in conversations by month three or four. If it shows you reaching break-even in month 17 with a healthy low point, you have far more freedom to choose your timing.

How much to raise

The same model answers this question. Decide the milestone the next round needs to reach, usually a revenue level or a set of metrics that supports the following raise. Project the cash you'll burn getting there, with your hiring plan included. Add a buffer, often six months or so of burn, for things that go slower than planned. That total is your floor. Raising meaningfully less than that means planning your next raise before you've hit the milestone.

Run it in a few scenarios: base case, slower sales, and a version with a hiring delay. If the amount only works in the optimistic case, it isn't enough.

Levers that extend runway

• Hiring dates. Pushing planned hires out by one quarter is often the single biggest lever, and it's reversible.
• Collections and billing terms. Faster collections and annual prepayment offers bring cash forward.
• Vendor review. Unused software seats and overlapping tools add up, especially after a year of growth.
• Marketing efficiency. Cutting the lowest-performing channels usually costs less growth than an across-the-board cut.
• Financing. Venture debt or a credit line can add months, at the cost of covenants and interest. Arrange it while you're in a strong position.

Runway mistakes that catch founders out

• Using gross burn for the headline and net burn in private. Pick one definition, say which one it is, and use it everywhere. Investors will ask.
• Counting money that isn't there yet. A signed term sheet isn't cash. A tranche that depends on hitting a milestone isn't cash until the milestone is hit.
• Ignoring payroll timing. If you pay twice a month, the month with three paydays in your bank statement can look like a spike that isn't really one, and the opposite can hide a real one.
• Forgetting annual and quarterly payments. Insurance, software renewals and taxes can take a large bite out of a single month near your low point.
• Assuming growth continues without cost. Revenue growth in the projection usually needs marketing and sales spending to keep going. If the model grows revenue while cutting acquisition spend, it's probably optimistic.
• Not updating after a big decision. A new office lease or a senior hire should trigger a recalculation the same week, not at the next board meeting.

Each of these can shift the cash-out date by a month or more, and a month matters a lot when you're timing a raise.

Keeping runway current

Runway isn't a number you calculate once for a pitch deck. Recalculate it every month after the books close, compare it with last month's projection, and look at why it moved. If it shortened, was that a decision you made, or something that happened to you?

Budgeter keeps runway live: it reads your accounting and bank data read-only, projects cash forward with your hiring plan and scenarios, and shows runway, cash-out month, break-even month and cash needed after every sync. You can test any decision against it by asking the AI CFO in plain English. Plans are listed on the pricing page.

Whatever tool you use, the habit is what matters: a projected cash curve, reviewed monthly, with the raise timed off the real cash-out date rather than the hopeful one.