Burn Rate and Cash Runway: How to Calculate Both

Burn rate is how much cash a business spends each month. Gross burn is total monthly cash outflow. Net burn is outflow minus cash collected from customers. Cash runway is how many months you can last: current cash divided by monthly net burn. If you hold $600,000 and net burn is $50,000, runway is 12 months.

Startups talk about burn constantly, but the idea matters to any business that is not yet profitable, is investing ahead of revenue, or is going through a slow season. This guide explains the formulas, works through a full example, and shows practical ways to slow the burn and stretch your runway.

Burn rate vs runway: the two numbers you need

The two figures answer different questions:

• Burn: how fast is cash leaving the business each month?
• Runway: at that pace, how long until the bank balance hits zero?

You need both. A high burn is fine if you have a large cash cushion and a clear plan. A small burn can still be dangerous if your balance is nearly empty. These metrics are cash measures, so they belong next to your cash flow forecast rather than your profit and loss statement.

Gross burn vs net burn

Measure	Formula	What it tells you
Gross burn	Total cash paid out in the month	The size of your cost base
Net burn	Cash paid out - cash received from customers	How fast your cash balance is actually falling
Cash runway	Cash balance / average monthly net burn	Months until cash runs out at the current pace
Burn multiple	Net burn / net new annual recurring revenue	How efficiently spending turns into growth (used mainly by SaaS investors)

Gross burn is useful for planning cuts because it shows the full cost base. Net burn is the number that drives runway. If revenue suddenly stopped, gross burn would become your net burn, so it is also a good stress test.

The runway calculator formula

The basic runway calculator formula is:

Runway (months) = current cash balance / average monthly net burn

Three refinements make it more reliable:

1. Average several months. Use a three-month average of net burn. One month can be distorted by an annual insurance payment or a large customer paying early.
2. Use cash, not accruals. Take figures from bank statements or your cash flow statement. Revenue that is invoiced but unpaid does not count.
3. Include all cash outflows. Loan repayments, equipment purchases and tax payments do not always appear as expenses on the P&L, but they reduce cash. If your books use accrual accounting, see cash vs accrual accounting for the difference.

Worked example: calculating burn and runway

Consider a small software startup with $600,000 in the bank at the start of July. Here are the last three months, taken from the bank account. All figures are illustrative.

Month	Cash out (gross burn)	Cash in from customers	Net burn
April	$86,000	$41,000	$45,000
May	$92,000	$40,000	$52,000
June	$92,000	$39,000	$53,000
Average	$90,000	$40,000	$50,000

Step by step:

1. Average gross burn = ($86,000 + $92,000 + $92,000) / 3 = $90,000 a month.
2. Average net burn = ($45,000 + $52,000 + $53,000) / 3 = $50,000 a month.
3. Runway = $600,000 / $50,000 = 12 months.

Now run two scenarios.

Scenario A: cut costs. The founders cancel unused software, sublet spare desk space and pause one planned hire, cutting $10,000 a month of outflow. Net burn falls to $40,000 and runway becomes $600,000 / $40,000 = 15 months. Three extra months bought without raising a cent.

Scenario B: lose revenue. A large client worth $12,000 a month leaves. Net burn rises to $62,000 and runway shrinks to about 9.7 months. That is why a single month of figures can be misleading, and why you should update the calculation every month.

Scenario C: revenue stops. If all customer cash stopped, net burn would equal gross burn of $90,000 and runway would be under seven months. It is a worst case, but it shows how exposed the business is.

Run the same scenarios whenever something material changes, such as losing or winning a large client, signing a lease or making a hire. Write down the assumptions next to each scenario, for example the date a client is expected to pay or the start date of a new employee, so you can check later which assumptions were wrong. Over time this makes your runway estimates more accurate and your decisions faster.

Why unpaid invoices quietly increase your burn rate

Many small businesses look healthy on paper because sales are invoiced, yet the bank balance keeps falling. The gap is usually receivables. If clients take 60 days to pay, the cash you need this month is still sitting in their accounts.

Two metrics help here:

• Days sales outstanding shows how long, on average, customers take to pay you.
• The cash conversion cycle shows how long cash is tied up between paying suppliers and collecting from customers.

Reducing collection time is the cheapest way to cut net burn. Send invoices the day work is delivered, state a clear due date, and follow up promptly. Our guide on how to get paid faster covers the practical steps. You can create professional, numbered invoices in minutes with the free invoice generator, which builds a PDF in your browser that you download and send yourself.

How to reduce burn and extend runway

Work through the levers roughly in this order, from least to most painful:

1. Collect faster. Chase overdue invoices, shorten payment terms for new clients and ask for deposits on large projects. See deposit invoices for how to bill upfront.
2. Review recurring costs. Cancel software nobody uses, downgrade plans and check every subscription on the card statement.
3. Renegotiate. Ask suppliers and landlords for better terms. Longer supplier payment terms move cash outflows later.
4. Delay discretionary spending. Pause events, office upgrades and experimental marketing that has not proved its return.
5. Slow hiring. Salaries are usually the largest cost. Each delayed hire saves the full monthly cost of that role.
6. Raise prices. A modest price rise on existing customers can cut net burn noticeably with little extra cost.
7. Bridge financing. If needed, options like invoice factoring or a credit line can smooth gaps, at a cost.

Avoid cuts that damage revenue, such as removing the people who deliver work to paying clients. A lower burn rate is only useful if the business can still grow or reach profitability.

How much runway is enough?

There is no official benchmark. In venture-backed startups, founders commonly aim for something like 12 to 24 months of runway after raising money, and begin fundraising well before runway drops below six to nine months, because raising money can take a long time. A self-funded service business with steady clients might be comfortable with three to six months of costs in reserve.

Think about:

• How predictable your revenue is. Retainer and subscription income is steadier than one-off projects.
• How fast you could cut costs if a large client left.
• How long it would take to raise money or arrange a loan.
• Seasonality. A business that earns most of its revenue in one quarter needs a bigger cushion for the quiet months.

Worked example: when to start raising or cutting

Back to the startup with 12 months of runway at $50,000 net burn. Suppose the founders estimate that raising a new round will take about six months from first meeting to money in the bank, and they want at least three months of cushion left when it closes. Working backward:

1. Required buffer at close: 3 months.
2. Time to raise: 6 months.
3. Latest safe start: when runway reaches 3 + 6 = 9 months.

With 12 months of runway today, they have about three months before they must start fundraising. If net burn creeps up to $60,000, runway drops to 10 months and that window shrinks to one month. The same logic applies to a bank loan or a cost-cutting plan: decide in advance the runway level that triggers action, and write it down so the decision is not delayed when the moment comes.

Seasonal businesses

A landscaping firm, a tour operator or a gift retailer may burn cash for several months and then earn most of its revenue in a short season. For these businesses a simple average can mislead. Instead, project each month separately for the next 12 months: expected cash in, expected cash out and closing balance. The lowest closing balance in the year is the number to watch.

For example, a business with $80,000 in the bank in October that expects net burn of $15,000 a month from November to February would reach a low of $20,000 at the end of February, before spring revenue arrives. If an unexpected $25,000 equipment repair landed in January, it would run out of cash. That is the case for building a seasonal reserve, or arranging a credit line before the quiet months rather than during them.

Tracking burn rate monthly

A simple routine keeps the numbers honest:

1. At month end, export bank transactions and total cash in and cash out. Many teams do this as part of a month-end close checklist.
2. Calculate gross burn, net burn and the three-month average.
3. Update runway with the current cash balance.
4. Note one-off items separately so you can see the underlying trend.
5. Compare against your small business budget and explain any big variances.

A simple spreadsheet is enough. Use one row per month and columns for opening cash, cash in, cash out, net burn, three-month average net burn, closing cash and runway in months. Add a notes column for one-off items such as an annual insurance premium, a tax payment or a large customer prepaying a year in advance. When you review the sheet, look first at the trend in the three-month average rather than any single month.

Plotting runway on a simple chart each month makes trends obvious. If runway is shrinking faster than planned, act early. Cutting costs with nine months of runway is far easier than with three.

Burn rate and profitability metrics

Burn tells you about cash, not profitability. A company can have positive EBITDA and still burn cash if it is buying equipment, repaying loans or waiting on slow-paying customers. Equally, a business can be loss-making on paper but cash positive for a while if customers prepay annual subscriptions.

That is why burn sits alongside other metrics. Unit economics tell you whether each sale makes money. Break-even analysis tells you how much revenue you need to stop burning. Together they show whether burn is buying sustainable growth or just delaying a problem.

If your cash position is tight, speak to an accountant or financial adviser before taking on debt or making major cuts.

Conclusion

Burn rate is the monthly speed at which you use cash. Gross burn shows your full cost base; net burn shows how fast the balance falls. Divide cash by average net burn to get runway, update it every month, and act while you still have time. Faster collections are the easiest win, so send clear invoices promptly with our free invoice generator.