You have an idea for a business, but making it a reality will necessitate you quitting your job. It's a big risk, considering your current gig means a steady paycheck that finances your life. So how do you know when to take the plunge? Take some tips from Stu Libby, co-founder of on-demand prescription-medication delivery service Zipdrug, which has been growing consistently week over week since coming out of beta in New York City last month. A former Google employee who left in 2009 to work on a startup, Libby points to several signs that can indicate now is the time to quit your job to pursue your passion.

You're not a hostage to your salary.

As people progress through life, they typically accumulate expensive things and incur debt, not to mention a growing family that needs to be fed, clothed, and sheltered. If that's you, spend some time thinking about how you can lower your expenses. Libby and his pregnant wife did it by moving from an expensive and tiny Manhattan apartment to a larger space in New Jersey. They also bought a more economical car and started sticking to a budget, which meant less eating out, buying clothes, and traveling.

You have a source of money outside of your big idea.

Either you live with someone willing to be your breadwinner for a period of time or you've accumulated a decent amount of savings. In Libby's case, his wife will take maternity leave once their child enters the world, but after that, she plans to return to work, so the family has a steady income.

You can't get your idea out of your head.

"It's like it just eats away at you more and more," Libby says. "If you say 'Oh, it's crazy. It's high risk. I can't do that,' but the idea keeps coming back, you have no control over it--I think that's a good sign."

Smart people think your idea will work.

Whether it's investors, co-founders, or anyone educated about the field you want to enter, if these people are authentically excited about your potential business it's a good sign.

Market research indicates people need what you want to build.

Market research doesn't need to be a large investment. Libby spent a few hundred dollars on a Google Consumer Survey, which polled people in New York about whether or not they would pay a certain amount of money for same-day delivery of their medications though an app. "We had a very favorable response from that survey," he says. "That was confidence-boosting because [it was] without anyone knowing the concept of what we're doing, without us spending any dollars on awareness marketing advertising."

You have mentors who will guide you.

Ideally, they have business experience and can give you valuable advice. "Sometimes, when I just hear myself articulating what's going on and the situation, the decisions are easier," he says. "You're not in your own head making a decision. You're hearing yourself talk out loud, and that's also proven to be extraordinarily helpful."

You have a co-founder who possesses strengths or connections you lack.

One of Libby's co-founders went to medical school and another has experience building tech startups. "We all have different areas of expertise, so we're able to divide and conquer," he says. "I wouldn't want to be doing this alone."