How do you calculate cash runway for a small business?

What Cash Runway Actually Means

Cash runway is the number of months a business can continue operating before it runs out of money, assuming no additional income or financing comes in. For a small business owner, this figure acts as a blunt but honest clock ticking in the background of every decision. The calculation itself is straightforward: divide your current cash balance by your average monthly net burn rate, and the result is the number of months you have left. If a business holds $60,000 in its operating account and spends $10,000 more than it earns each month, the runway is six months. That number can shift dramatically depending on whether you are looking at gross burn, which counts all outgoing expenses, or net burn, which subtracts revenue from total expenses. Many small business owners confuse the two and end up with a dangerously optimistic picture of their financial health.

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The Core Formula and What Each Number Represents

The standard formula for calculating cash runway is Cash Runway (months) = Current Cash Balance ÷ Monthly Net Burn Rate. The current cash balance should include money in checking accounts, savings accounts, and any short-term instruments that can be converted to cash within a few days without penalty. The monthly net burn rate is the difference between total monthly cash outflows and total monthly cash inflows from operations. For example, if a business has $45,000 in cash, pays $8,000 in rent and payroll each month, and generates $3,000 in revenue, the net burn is $5,000 per month and the runway is nine months. Some analysts prefer to use a trailing twelve-month average for the burn rate rather than a single month, because one unusual month can distort the picture. A business that spent $15,000 in January due to a one-time equipment purchase but typically burns $8,000 per month would show a misleadingly short runway if January were used alone.

Step-by-Step Process for an Accurate Calculation

Start by pulling your bank and payment processor statements for the last three to six months to establish a reliable baseline. List every recurring outflow, including rent, utilities, subscriptions, payroll, vendor payments, loan repayments, and taxes set aside. Then list every inflow, including customer payments, recurring revenue, and any side income. Subtract total monthly outflows from total monthly inflows to get the net burn for each month. Average those monthly net burn figures to smooth out seasonal spikes or one-off anomalies. Divide your current cash balance by that average monthly net burn to arrive at your runway in months. It is wise to run this calculation twice: once using actual bank balances and once using a conservative estimate that assumes some receivables might be delayed by 30 to 60 days. This dual approach helps you avoid the trap of counting money that has been promised but not yet received.

Why Gross Burn and Net Burn Tell Different Stories

Gross burn measures the total amount of cash a business spends each month regardless of revenue, while net burn subtracts operating revenue from those expenses to show the actual cash lost each month. A business with $12,000 in monthly gross burn and $7,000 in monthly revenue has a net burn of $5,000. If that business holds $30,000 in cash, its runway based on gross burn is 2.5 months, but its runway based on net burn is 6 months. The difference matters enormously for planning. Gross burn is useful for understanding the absolute cost of keeping the lights on and for comparing businesses with different revenue profiles, but net burn is the figure that determines how long you can survive without new funding. Investors and lenders typically focus on net burn when evaluating a company's runway, because it reflects the real rate at which cash is disappearing.

Common Mistakes That Distort the Runway Calculation

One of the most frequent errors is using a single month's data instead of a rolling average, which can make a business look like it has more or less runway than it actually does. Another common mistake is forgetting to include irregular but predictable expenses, such as annual insurance premiums, quarterly tax payments, or yearly software license renewals, which can spike the monthly burn rate in certain periods. Some business owners exclude debt repayments from their burn calculation, treating them as non-operational, but debt repayments are cash outflows that reduce the balance in the operating account and should be included. Failing to account for delayed customer payments is another trap, especially for businesses that invoice on net-30 or net-60 terms. If your books show $50,000 in accounts receivable but your bank account shows $5,000, your actual cash runway is far shorter than the receivables suggest. Finally, ignoring the impact of seasonal revenue swings can lead to a runway estimate that holds true in peak season but collapses during the slow months.

When to Act Based on Your Runway Number

A cash runway of fewer than three months should trigger immediate action, such as cutting non-essential expenses, accelerating collections, or seeking a line of credit or bridge financing. A runway between three and six months is a warning zone that calls for a detailed review of spending and a plan to either increase revenue or reduce the burn rate. A runway of six to twelve months provides a comfortable window to pursue strategic growth, negotiate better payment terms with vendors, or explore financing options without panic. Businesses that consistently maintain a runway of less than two months are operating in a fragile state where a single unexpected expense, a late customer payment, or a drop in revenue can push them into insolvency. Setting a target runway of at least six months is a common recommendation among financial advisors, though the right target depends on the stability of your revenue streams and the predictability of your expenses.

How AI Tools Like Glassjar Improve Runway Accuracy

Traditional cash runway calculations rely on manual data entry and spreadsheet formulas, which introduces human error and delays. An AI-powered cashflow and savings coach for SMBs automates the ingestion of bank transactions, categorizes expenses in real time, and continuously recalculates runway as new data flows in. Instead of waiting until the end of the month to discover that the burn rate was higher than expected, a business using an AI coach can see the trend forming within days and adjust spending before the runway shrinks dangerously. These tools can also run scenario modeling, showing what happens to runway if revenue drops by 10%, 20%, or 30%, or if a major expense is added. The transparency of AI-driven forecasting removes the guesswork and gives business owners a clearer, more current picture of their financial position than a static spreadsheet ever could.

Comparison: Manual Spreadsheet vs. AI-Powered Cash Runway Tracking

Begin by opening a dedicated spreadsheet or signing up for a cashflow tracking tool that connects to your business bank account. Record your current cash balance and list every recurring monthly expense and every source of monthly revenue. Calculate your net burn rate for the last three months and average them. Divide your cash balance by that average to get your current runway. Set a calendar reminder to repeat this calculation every month, and adjust your targets if your runway falls below six months. If you find the process tedious or error-prone, consider an AI-driven solution that handles the data ingestion and calculation automatically, freeing you to focus on acting on the numbers rather than compiling them.