As a 23-year-old editorial assistant living in New York City, I was confident in my relationship and in my reasons for wanting to move in with my boyfriend of two years. I'd become a bag lady lugging my life between our apartments just as the hobo chic look had lost its appeal. I dreaded forfeiting my monthly rent check—also known as half my salary—to keep a studio I never saw. And I knew I eventually wanted to marry my boyfriend—just not yet.

But I hadn't considered the financial commitment of moving in together until I rode up 14 flights between my boyfriend Zach and the building's blonde broker and walked into the perfect place to live in sin. Although the apartment was everything we wanted—endless closet space, a dishwasher, sparkling hardwood floors and steps from multiple subways—it was out of my price range.

"The only way we'll find an apartment you can afford is if we move to Weehawken, New Jersey," Zach said. He was right.

Suddenly, our new relationship status felt plagued by monetary challenges. Zach's private equity salary was three times higher than my publishing paycheck, and I didn't know how I'd feel like an equal partner if I depended on him for money. Although I'd come to terms with my pathetic income, I didn't want Zach to see me as needy. I knew our relationship would have to shift, but all the movement was making me uneasy.

With a little research, I learned I wasn't alone in my reservations. According to Joselin Linder and Elena Donovan Mauer's book The Good Girl's Guide to Living in Sin, "Money in particular evokes emotions that are learned throughout your life. It brings up powerful stuff like anxiety and, in some cases, terror." The guide to moving-in also lists saving money as one of the most common reasons couples decide to live under one roof before marriage and "it isn't unusual for one half of a couple to earn more than the other."

I feared my prorated rent would eliminate my right to whine about Zach's choice of $1.99 V05 shampoo or to splurge on my $15 curly girl products. More importantly, I didn't want Zach to dictate my spending or resent me for choosing new gold peep-toes over dinner out.

So before you book a truck and start unpacking, you need to have a plan. There isn't a "right" strategy to manage your financial arrangement, but a successful live-in relationship is more likely with an agreement. Whether it's in an Excel spreadsheet or not is up to you, but make sure it's written down. If you know a notary or have a lawyer friend its even better if they can make it official.

Start with your biggest shared expense, which is most likely rent. For Leah, 25, a teacher and Mike, 25, an urban planner it wasn't as simple as dividing this monthly cost in half:

"When he first moved in, I had been working for a year and he was straight out of college without a job. We had a gradual split-rent plan, meaning the first month he paid a small amount of the rent, the next month a little more, and so on until we were splitting the cost of rent." Part of living together is stretching yourself to help out your partner.