A S BANKA ADVISORS

Key Takeaways

• Gross burn is the total cash you spend each month. Net burn is gross burn minus the cash you collect. Runway is built on net burn, not gross.
• Runway = current free cash divided by average monthly net burn. It tells you how many months you can operate before you run out of cash.
• The single biggest error is calculating runway on the bank balance instead of free cash: taxes collected, taxes withheld, and customer advances are sitting in the account but are not yours to spend.
• Use a trailing 3-month average for net burn, not your best or worst single month, so one large payment does not distort the number.
• Track runway monthly. The day to raise or cut is decided by the trend in your burn, not by the balance on any single morning.

What Are Burn Rate and Runway?

If you want to know how to calculate burn rate and runway for your startup, start with what each number actually measures. Burn rate is how fast your company spends cash. Runway is how long that cash will last at the current rate. Together they answer the only question that matters when you are not yet profitable: how many months do I have before I either turn cash-positive or need more money?

Almost every founder can quote their bank balance. Far fewer can tell you their net burn and their runway with any confidence, and those are the two numbers that decide when you hire, when you cut, and when you start a raise. Getting them wrong is how a company that “had plenty of cash” finds itself with eight weeks of runway and no warning.

Gross Burn vs Net Burn: The Difference That Trips Founders Up

There are two burn numbers, and confusing them is the most common mistake.

Gross burn is the total cash going out of the business every month: salaries, rent, software, marketing, contractors, everything. It is what you spend regardless of what you earn.

Net burn is gross burn minus the cash that comes in from customers. If you spend Rs 20 lakh a month and collect Rs 8 lakh from customers, your gross burn is Rs 20 lakh but your net burn is Rs 12 lakh.

Runway is always built on net burn, because the cash you collect genuinely extends how long you last. A founder who plans on gross burn will be too conservative and may raise or cut earlier than needed. A founder who ignores burn entirely and just watches the balance will be caught out when a big quarterly payment lands.

The Formulas

• Gross burn = total cash outflows in the month
• Net burn = gross burn minus cash collected from customers in the month
• Runway (months) = current free cash divided by average monthly net burn

The word doing the heavy lifting is free cash, not total cash. We will come back to it, because it is where most runway calculations quietly go wrong.

A Worked Example

Here is a simple monthly picture for an early-stage Indian startup.

Now suppose the bank account shows Rs 1,20,00,000 (Rs 1.2 crore). The tempting calculation is Rs 1.2 crore divided by Rs 12 lakh net burn, which gives 10 months of runway. That number is almost always too optimistic, and the next section explains why.

Why Founders Get Runway Wrong: Bank Balance Is Not Free Cash

The error is using the bank balance in the runway formula instead of free cash. A chunk of the money sitting in your account is not yours to spend. It typically includes:

• GST collected from customers that you owe to the government on the next filing.
• TDS deducted from vendor and salary payments that you have to deposit.
• Customer advances for work you have not delivered yet, some of which could be refundable.
• Accrued bills already incurred but not yet paid.

Suppose Rs 25 lakh of that Rs 1.2 crore is taxes collected, taxes withheld, and undelivered advances. Your real free cash is Rs 95 lakh, not Rs 1.2 crore. Divide Rs 95 lakh by Rs 12 lakh net burn and your true runway is closer to 8 months, not 10. Two months of runway vanished the moment you used the right number, and two months is the difference between a calm raise and a panicked one.

How to Calculate Your Burn Rate and Runway: A 5-Step Process

1. Add up gross burn for the last three months. Take total cash outflows for each of the last three months and average them. Three months smooths out one-off payments like an annual software renewal or an advance tax instalment.
2. Subtract cash collected to get net burn. For each of those three months, subtract the cash you actually collected from customers, then average. Use cash received, not invoices raised.
3. Work out your free cash. Take the bank balance and subtract what is not yours: GST collected, TDS deducted but not deposited, refundable customer advances, and bills already due. What is left is free cash.
4. Divide free cash by average net burn. That is your runway in months. If free cash is Rs 95 lakh and net burn is Rs 12 lakh, runway is roughly 8 months.
5. Recalculate every month and watch the trend. A single month tells you little. A runway that shrinks from 10 to 8 to 6 over three months is the real signal to act, well before the cash actually runs low.

If you are running these numbers because a raise is on the horizon, it also helps to frame the ask realistically. Our free Startup Valuation Estimator can give you a directional sense of how your runway and traction translate into a valuation range before you walk into an investor conversation.

When Should You Act on Your Runway?

A widely used rule of thumb is to begin a fundraise when you have roughly six months of runway left, because raising itself often takes three to six months. If your runway is falling and you are below that mark, you have two levers: increase the cash coming in, or reduce gross burn. The earlier you see the trend, the more calmly you can pull either one. Founders get into trouble not because they run out of cash suddenly, but because they were watching the bank balance instead of the runway trend.

The size and timing of that raise is also an equity decision, not just a cash one. Understanding how dilution interacts with your raise helps you avoid solving a short runway with terms you regret later. Remember too that your ESOP pool is a real cash and equity cost that shapes how much you actually need to raise.

Frequently Asked Questions

What is a good burn rate for an early-stage startup?

There is no single “good” number, because it depends on your stage, sector, and how much you have raised. The useful test is not the size of the burn but the runway it produces and what you are getting for it. A high burn that is buying real growth and at least 12 months of runway is very different from the same burn with 4 months of runway and flat revenue, which is exactly why investors look past the headline burn to the numbers investors actually test.

What is the difference between gross burn and net burn?

Gross burn is your total monthly cash spend. Net burn is gross burn minus the cash you collect from customers in the same month. Runway is calculated on net burn, because the cash you bring in genuinely extends how long your money lasts.

How do I calculate runway?

Runway in months equals your current free cash divided by your average monthly net burn. The key is to use free cash (bank balance minus taxes collected, taxes withheld, and refundable advances), not the headline bank balance.

Why is my real runway shorter than my bank balance suggests?

Because part of your bank balance is money you are only holding: GST collected, TDS deducted, and customer advances for undelivered work. Subtract those before you calculate runway, or you will overstate how long your cash will last.

How often should I calculate burn and runway?

Every month. The decision to raise or cut is driven by the trend in your burn and runway over several months, not by the balance on any single day.

The Bottom Line

Burn rate and runway are not advanced finance. They are two arithmetic numbers every founder should be able to state on demand. Calculate net burn on a trailing three-month average, build runway on free cash rather than the bank balance, and recalculate monthly so you act on the trend. Do that and you will never be the founder who was surprised by a cash crunch that the numbers had been signalling for months.

Disclaimer: This article is for general educational purposes and does not constitute financial, tax, or investment advice. Figures used are illustrative. Consult a qualified professional about your specific situation.