# Burn and Runway: Simple Numbers Every Solo Founder Needs

*5 November 2026 · Proven Founder blog*

**Short answer:** Burn is the net cash you spend each month after receipts, runway is that cash divided by the burn to show how many months you can keep operating. Compute from your bank balance and monthly spend, then share the two numbers plainly with a brief next-step note.

## Key takeaways

- Burn shows cash out minus cash in each month, runway shows how many months that cash will last.
- Use your bank start balance, list every payment and receipt, then subtract to get net burn.
- Divide the same balance by net burn to get runway, round down to whole months.
- Share the two numbers plainly, add a short plan, and keep the definitions identical every month.

## What burn and runway really mean

Burn and runway are the two cash health numbers that matter every month. Burn tells you how much cash leaves the business after you subtract any incoming money. Runway tells you how many months that cash will last if the burn stays the same. Both are simple to compute and easy to explain. They are not forecasts, they are current snapshots.

Because they are cash based they avoid the temptation to hide problems behind growth metrics. Investors look first for a clear burn number, then for a runway that gives them confidence you can keep operating while you hit next milestones. If the numbers are missing or change every update they create doubt. A steady format builds trust.

## How to calculate burn from a bank balance and monthly costs

Start with the cash you have in the bank on the first day of the month. Then list every cash outflow for that month: salaries, rent, tools, marketing spend, taxes, and any loan payments. Add any cash inflow you received that month, such as subscription revenue or one-off sales. Burn equals outflows minus inflows. If inflows are larger than outflows the burn is negative, meaning you added cash.

Put the numbers into a single spreadsheet row. Keep the same column names each month: “Bank start”, “Total outflow”, “Total inflow”, “Net burn”. Do not change the definition of net burn from month to month. A verified number comes directly from the table; a stated number is a calculation you performed. Mark which is which if you share the sheet.

- Look at the opening balance on the first day
- Add every payment you made that month
- Add every receipt you earned that month
- Subtract receipts from payments to get net burn
- Record the result in a table you reuse

## How to calculate runway from burn

Runway is simply the cash you have divided by the net burn you just calculated. Use the same bank start amount you used for burn. If the net burn is zero or negative the runway is effectively unlimited for now, but you should still track the number. Write the result as a whole number of months.

Put the runway next to the burn in the same spreadsheet row. This lets you see at a glance whether you need to tighten spend or raise money. If the runway is less than a few months you can start a conversation with investors early, before the number becomes a crisis. If it is many months you can stay focused on product work.

- Take the opening balance
- Divide by net burn
- Round down to whole months
- Record alongside burn each month

## How to present burn and runway without alarm

When you write an investor update, lead with the headline “Current burn is X and runway is Y months”. Keep the tone factual. Do not add adjectives that suggest panic or triumph. The numbers speak for themselves. If the runway is short, add a short line about the plan you are executing to extend it.

Add a one-sentence “What’s next” that ties the numbers to concrete actions. For example, “We are cutting non-essential SaaS licences and negotiating a longer contract with our biggest client”. This shows you are actively managing cash. It also gives investors a clear signal that you are on top of the situation, not ignoring it.

## How to keep the numbers useful month to month

Stick to the same definitions every month. Do not swap “total cash outflow” for “operating expense” unless you note the change. Consistency lets you spot trends and lets investors trust the data. If you need to add a new metric, add it in a separate column rather than replacing an existing one.

Update the spreadsheet at the end of each month, not later. Send the new row to investors with your regular update. Treat the numbers as a conversation starter, not a final verdict. Over time you will see the effect of decisions, and you can adjust spend before the runway shrinks to a dangerous level.

## Common pitfalls to avoid

A common mistake is to use gross cash outflow instead of net burn. Gross numbers hide the effect of new revenue and make runway look shorter than it actually is. Another mistake is to change the definition of burn after a bad month to hide a rise. Consistency beats clever re-labeling.

Do not put sensitive customer data or contract values in the public version of your update. Do not compare runway to an industry average that you cannot verify. Do not claim that you will never run out of cash; say you are monitoring it each month. These habits keep the conversation honest and protect you from needless panic.

## Questions people ask

### What if my net burn is negative?

A negative net burn means you added cash during the month. It shows you are growing the bank balance rather than shrinking it. In an update you can note the negative burn and explain which revenue stream caused the cash inflow. It still makes sense to calculate runway, but the result will be a very high number or undefined if you keep adding cash.

### How often should I calculate and share these numbers?

Most founders update them at the end of each month. That cadence matches most reporting cycles and lets you catch a problem early. If you are in a rapid growth phase you can do a quick check every week for yourself, but the public note can stay monthly. Consistency matters more than frequency.

### Should one-off sales be included in the burn calculation?

One-off sales are part of cash inflow, so they belong in the same month they are received. They reduce the net burn for that month. Do not count them as recurring revenue when you talk about MRR, but they still affect the cash balance you are tracking for runway.

### How do I talk about a runway that is only a couple of months without scaring investors?

State the runway number plainly and then add a short plan. For example, “Runway is two months. We are finalising a term sheet with an existing investor and have a sales pipeline that should close next quarter.” The plan shows you are not passive and gives investors a path to help if needed.

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