How to Calculate Runway

1. What Runway Actually Measures

Runway is the number of months until cash reaches zero at the current rate of consumption. It is a forward-looking estimate, not a historical measure, which is why the inputs matter so much.

Burn rate vs runway confuses people because they are related but answer different questions. Burn is how fast money leaves. Runway is how long before it runs out.

2. Why Averages Produce the Wrong Answer

A twelve-month average smooths exactly the trend you need to see. A business whose burn rose from $60,000 to $140,000 across a year has an average near $95,000 and a current reality far worse.

The same applies in reverse. A company that cut costs three months ago will understate its runway using a yearly average, which leads to unnecessary caution.

A startup runway calculator using average burn will give a confident answer to the wrong question. Use the last three months and look at the direction of travel.

• Averages hide trends, which is exactly what matters for a forward estimate
• Rising burn means an average overstates runway, often badly
• Falling burn means an average understates it and prompts over-caution
• Committed future spend is invisible in any historical figure

3. How to Pick the Right Burn Figure

Use net burn, which is cash out minus cash in, over the last three months. Then adjust for anything known about the next three that differs.

Gross burn, which is simply cash out, is useful for understanding cost base but overstates consumption for any business with revenue.

• Net burn: cash out minus cash in, the figure runway should use
• Gross burn: cash out only, useful for cost base analysis
• Three-month window: recent enough to be current, long enough to smooth noise
• Adjust forward for known hires, contract starts and one-off costs
• Recalculate monthly, because the answer moves

4. 7 Steps to Calculate Runway Accurately

Step three is where most calculations go wrong. The rest are adjustments that refine it.

Step 1: Establish Available Cash

Bank balances minus anything restricted, held as security, or already committed to a specific payment. Available cash is usually lower than the headline bank figure.

Step 2: Exclude Money You Do Not Control

Customer deposits held against future delivery, payroll tax withheld and not yet deposited, and sales tax collected are not yours to spend. Counting them inflates runway.

Step 3: Calculate Net Burn Over Three Months

Cash out minus cash in for each of the last three months. Look at the three figures individually before averaging, because a trend tells you more than the mean.

Step 4: Adjust for Known Changes

Hires starting, contracts ending, annual payments falling due. A model that uses only historical burn misses every change the founder already knows is coming.

Step 5: Time Receivables Realistically

Expected collections belong in the forecast at their realistic date, not their invoice date. A ninety-day payer should be modelled at ninety days regardless of the terms on the invoice.

Step 6: Divide and Sanity-Check

Available cash divided by adjusted monthly net burn. Then check the answer against the bank balance trend over the last six months. If the two disagree, an input is wrong.

Step 7: Build the Downside Case

Recalculate assuming revenue is twenty percent below plan. Runway planning services exist largely to make this a routine exercise rather than a crisis response.

How to calculate runway honestly means knowing both numbers: the planned case and the case where things go slower than hoped.