Quick math problem: while camping, you decide to start a fire. You have five logs. Three are needed to start the fire. Each log will burn for roughly one hour. How long will your fire burn before more logs are needed?

The answer is your burn rate. It’s a simple measure of how fast you consume available resources. And it greatly affects your professional and personal future.

In a business context, burn rate refers to negative cash flow that is usually experienced as part of a startup enterprise. Whether you plan on making something, provide a service or some combination of the two, you will need money to get up and running. And if you exhaust your cash reserves before turning a profit, you’ll need to obtain additional funding (take a loan, sell equity, offer stock, etc.) or shutdown operations. Thus, your firm’s burn rate determines how long you can survive without making a profit.

Businesses with excessively high burn rates require a lot of cash, which is problematic for entrepreneurs, worrisome for investors and potentially terminal for employees. Out of control burn rates plagued my career for the better part of a decade, particularly during my final months with a dying dot.com. Many believed the Internet would universally increase gross revenues (when it in fact would universally decrease transaction costs), and my employer had capitalized on the feverish race to the Internet and speculative investing to artificially inflate the wealth of its VPs and executives.

But when the bubble burst and more venture capital was nowhere to be found, we began laying off sales and customer service associates with regularity. In my new role as “Director of No Sales”, I repeatedly explained the layoffs using the company line: “…necessary restructuring in an effort to lower the corporate burn rate.” Eventually I placed myself on the chopping block, took my small severance and moved on. I was young and inexperienced, but the situation was not unique.

In a health context, burn rate refers to how many calories you consume over a period of time for a given activity. Whether you plan on running a marathon, play some golf or relax in a hammock, you will need some fuel to keep your body operational.  And if you burn less than you take in, your body will convert the excess to fat and store for future use. Thus, your body’s burn rate determines how much you can eat without gaining weight.

Individuals with morbidly low burn rates require a lot of restraint, which is problematic for dieters, worrisome for spouses and potentially terminal for food lovers. An imbalanced burn rate caused me to gain 70+ pounds over the course of a decade. Most of it was acquired during times of stress and anxiety, such as the two years spent attending night classes in pursuit of an MBA.

I had no interest in a four or five year endeavor that slowly acquired credits; I preferred to get it done as fast as possible and therefore attended classes four nights a week while working full-time. It left little opportunity for much of anything else, especially exercise. A ridiculously low burn rate coupled with lots of fast food and late night snacking eventually bloated my midsection. I was older and more educated, but the situation was not unique.

So know your burn rate. It significantly affects your long term health—both professional and personal.