Henry Nadler* spends up to 12 hours a day working as a remote creative director, conceiving and executing campaigns for a New York–based ad agency — and his hard work shows up in his six-figure paycheck.

But instead of taking a load off at 5 or 6 p.m. to make dinner or hit the gym, Nadler, who is in his mid-30s and lives in Los Angeles, is getting ready for a second shift as the sole "ad agency" for a freelance client.

In this supplemental job, he does everything from account planning and strategic development to trafficking. And when he's not doing either of those jobs, there's a good chance he's tapping into his third income source: making extra money doing voiceovers for commercials.

Nadler admits he's an overearner, but says that making extra money is only a small part of why he overearns. His love of creative work is his primary motivation. And although he gets only about five hours of sleep most nights, he gives off the impression that he couldn't be happier.

"The way you make money is doing things you love, because it doesn't seem like work to you," says Nadler. "When this other opportunity came along, it felt amazing, because I knew they were going with me because of the ideas I was going to bring to the table."

Still, thanks to the extra money, he's able to afford a few nice perks — beyond fancy dinners out and nice vacations. Recently, he was able to finance his own independent production company, which he co-owns with his fiancée. He admits, though, that working three jobs does take a toll, both on his relationship and his ability to focus.

"There is a lot of travel, a lot of late nights, when I can't pay attention to home life and fun things the way someone in a more traditional work life could do," he says. "On Thursday nights, when people want to go out, or Friday nights or even some Saturday nights, I'm tired. So that can certainly put a strain on a relationship."

But Nadler isn't alone in working beyond his day job and burning the proverbial candle at both ends, especially in an uncertain economic environment. The lingering threat of joblessness combined with increasing costs (health care, housing, college etc.) can spur many people to strive for extra cash to pad their wallets and assuage their fears.

So when does overearning cross that line to become good for your money, bad for your well-being?

Inside the mind of an overearner

Being an overearner is a bit like being a garden-variety workaholic — both tend to involve working far more than a 40-hour workweek — but the drives underlying each tend to differ. Whereas workaholics may put in extra time at work to escape something else, like a less-than-fulfilling relationship or social life, overearners are, at least partially, motivated by another paycheck.

Family clinical psychologist Gerald Grosso, clinical director of Newport Beach, Calif.–based Morningside Recovery, which specializes in treating addiction, says overearners are often motivated by a number of things, such as fear of not having enough money or fear of feeling inadequate.

Often times, as in Nadler's case, it isn't necessarily about need: Overearners can also earn extra paychecks in order to live more comfortably, not merely survive.

Kat Munson, a 28-year-old high school teacher in New Canaan, Conn., doesn't consider herself an "overearner" because she isn't necessarily rolling in the dough with her decent, but not grandiose, five-figure salary. But the additional $10,000 a year she makes after-hours as a coach for a handful of local high school swim teams, not to mention the thrill she feels coaching kids in her favorite sport, makes it hard to say no to the extra gigs.

"I probably wouldn't need the money if I was O.K. living paycheck to paycheck on my teaching salary, but I'm not," says Munson. "I have undergrad loans and graduate school to pay [for]."

By earning extra money, Munson doesn't have to stress as much about taking a vacation or enjoying a night on the town. She also can't seem to envision a life where she would just come home from work and go to happy hour like an ordinary person.

"I think, having been a swimmer and a student, I was always balancing doing a ton of different things," she says. "I was brought up not having free time, so I feel like in my head, people who aren't working are wasting time. What are you doing? What are you giving back?"

When is overearning a problem?

Plenty of Americans take on an extra paid gig here and there to accumulate a little fun money. But unlike regular, occasional-overtime workers, overearners are often motivated by a compulsive need to earn more, says Grosso. And it's when overearning interferes with your daily activities, such as getting adequate sleep or spending time with family, that it becomes problematic.

"You can get the same euphoric effect of substances [like drugs or alcohol] from accomplishment," says Grosso. "Once I start to accomplish a specific thing, I'm now starting to chase that feeling again. I've got to work more to create this over and over again. This is where it starts to cause disruption in other areas of my life, because now I'm not sleeping, or it's causing issues in my relationship."

Take Amber Simon*, 33, a physician in Detroit. In addition to her full-time job at a pediatric practice, she began doing moonlight shifts at a hospital downtown once a month. The patients were different, the job was more demanding, but what really seduced her was the fat bonus paycheck. Soon, Simon — who was in a new relationship — had signed on to work three out of four weekends a month and one overnight shift midweek.

While she was raking in the money, which helped pay down her credit card debt, her new boyfriend began to complain that he felt like a "widow" going solo to so many summer social events. Meanwhile, Simon was struggling to catch up on sleep lost to her overearning tendencies.

And the siren song of that extra earning power can get addictive: When overearners cut back, Grosso says, they sometimes experience withdrawal symptoms like that of an addict.

"You see people go through a crash no different than with some type of physical addiction," he says. In this case, "they get themselves in a position where they can't maintain the pace anymore."

How to strike a balance

Nadler says slowing down is always on his to-do list. But the projects he's assigned just keep getting better and better.

"It's a constant struggle, because you say, 'This project's done … now it's time to scale back a bit,'" he says. "But then you hear about the next commercial, and you say, 'Ah, I really want to do that!'"

Still, he says he's made some progress in finding balance. When he's at home and has finished working for the night, his computer stays shut. And, he says with a laugh, he never works on vacation.

Meanwhile, Munson says earning beyond Job #1 has taken somewhat of a toll on her social life. Like Simon, she doesn't get to spend as much time with her boyfriend as she'd like. But both say their overearning is a temporary state of affairs: They plan to scale back when they have kids one day.

For now, Munson says, her extra work also supplies something more than a paycheck that she couldn't get elsewhere: "There are definitely some days I'd prefer to just go home and hang out," she admits. "But there are other days, when these kids go over and hug you at the end of their swimming race, and it's worth all the hours you put in."

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