What Is Burn Rate?

Clarity over convention

The Sibyl Un-Glossary

Some terms have been defined in many places, yet misinterpretations of them keep appearing in decks. At Sibyl, we’re doing the un-glossary instead: starting with what a term is often mistaken for, then working toward what it actually means. We hope it helps.

Burn rate sounds like one of the simplest numbers in startup finance: how quickly is the company using up its cash? But a burn number can create false confidence surprisingly easily. It can describe what happened last month without telling you what happens next. It can count revenue that has not actually arrived. Or it can mean something completely different depending on whether someone is talking about gross or net burn. Because burn rate is usually translated directly into runway, small misunderstandings can become very large financing problems.

1. Today’s burn is not tomorrow’s burn

A burn rate is a snapshot, not a forecast.

Founders often calculate runway by dividing the cash in the bank by the company’s current monthly burn. That calculation is useful, but only if burn stays roughly the same.

Imagine a startup has $1.2 million in cash and is currently burning $100,000 per month. The simple calculation says it has 12 months of runway.

But the company has already committed to hiring four people over the next three months. Those hires will increase monthly burn to $140,000. It also has a $60,000 annual software and insurance bill due six months from now.

The company does not really have 12 months. Its future cash requirements have already changed, even though its current burn rate has not.

The mistake is not calculating burn incorrectly. It is assuming that a backward-looking number is also a forward-looking cash forecast.

2. Revenue is not cash

A sale does not reduce burn until the money actually reaches the company.

Startups often track ARR, MRR, bookings, invoices, and revenue alongside burn. That can make it tempting to subtract revenue from expenses when estimating how fast cash is disappearing. But burn is about cash.

Suppose a company spends $150,000 in March and invoices customers for $100,000. On paper, it may look as though net burn is only $50,000.

But those customers have 60-day payment terms and none of the $100,000 arrives during March. The company actually needs the full $150,000 of cash to get through the month.

Eventually the invoices may be collected and reduce future cash burn. But they cannot pay March payroll while they are still sitting in accounts receivable.

For founders, the difference between revenue earned and cash collected becomes especially important as companies grow, offer longer payment terms, or sign large enterprise customers.

3. Gross burn and net burn are not the same thing

“Our burn is $150,000” is incomplete unless everyone knows which burn you mean.

Gross burn measures how much cash a company spends. Net burn measures how much cash the company loses after cash coming in from customers is taken into account.

Consider a startup that spends $150,000 each month and collects $90,000 from customers. Its gross burn is $150,000. Its net burn is $60,000.

If the company has $600,000 in the bank, those two numbers create radically different impressions. Dividing cash by gross burn gives four months. Dividing it by net burn gives ten.

Both numbers can be useful. Gross burn tells founders how large the company’s underlying cost base is. Net burn tells them how quickly the cash balance is currently shrinking. The danger comes from using the word “burn” without knowing which one is being discussed.

Why does burn rate matter to early stage founders?

Burn rate is the bridge between a startup’s strategy and its bank account. Every hiring plan, product investment, marketing experiment, and expansion decision eventually changes burn. And burn, in turn, determines how much time the company has to reach the next milestone before it needs additional capital.

That makes burn especially important for venture-backed companies. A founder who believes the company has 18 months of runway may comfortably hire ahead of growth. A founder who realizes the real number is nine months may make a completely different decision.

Investors also rarely evaluate burn in isolation. The important question is what the company is buying with that cash: revenue growth, product progress, customer retention, technical milestones, or some other increase in enterprise value.

Low burn is not automatically good, and high burn is not automatically bad. Burn becomes dangerous when the company is consuming cash faster than it is creating the milestones needed to justify the next dollar of funding.

How wrong is too wrong?

Being slightly wrong about burn for a single month is usually harmless. Startup cash flows are noisy. Customers pay early or late, legal bills arrive unexpectedly, annual subscriptions renew, and hiring dates move around.

The problem begins when the error changes a founder’s view of runway. If management believes it has 15 months of cash when the realistic forecast says ten, that five-month difference can determine whether the company starts fundraising early enough, makes another round of hires, or discovers too late that it no longer has much negotiating leverage.

Burn rate does not need to predict the future perfectly. It does need to be accurate enough that the company does not confuse a hopeful financing timeline with the amount of time actually left in the bank.

What it actually means

Burn Rate

The amount of money a company consumes, usually measured monthly, quarterly, or annually. It is the net cash leaving the bank account over that period.