65% of unmarried millennial couples live together, but over half aren't sharing the cost equally

Moving in with your significant other can be exciting — both emotionally and financially. 

You're not only taking a big step in your relationship, but there's a good chance you as an individual may be able to cut down on some living expenses as a result of sharing costs with your partner.

It's common for millennial couples to move in together before they're married: 65% of unmarried millennial couples have already taken this step, according to a recent survey from the Thriving Center of Psychology. And a majority of them — 61% of cohabiting millennial couples — cite financial reasons as a contributing factor.

But many don't share costs equally: 52% of millennial couples who live together don't split their rent or mortgage payment evenly, the survey found.

And not every couple is happy with their setup. More than 1 in 3 couples surveyed said they felt financially unequal in their relationship.

Money can be a tricky subject to discuss with your significant other, but it's important to talk about, especially if you live together. How much will each person contribute to the bills? How will you handle discretionary spending when you do things together?

Here are three tips for managing your money as a couple to help take some of the stress out of moving in together.

1. Organize your shared expenses

You get groceries, I'll cover takeout. You pay for the pet insurance, I'll cover the internet bill. Every couple has their own method for splitting costs, but however you and your partner decide to pay for things, it's a good idea to keep track. 

Kelly Klingaman, a certified financial planner based in Austin, Texas, who works with professional women and dual-career couples, says she often sees clients who routinely Venmo each other back and forth for things. They may have a spoken or unspoken agreement to share costs and pay each other back for things like utility bills and groceries, but "it seems really disorganized," she tells CNBC Make It.

"They were just going through the motions of what they've been doing since the early days of dating where they were paying each other back via Venmo," Klingaman says. "And now years later, they're still doing the same thing and wondering why it feels off and why they're stressed out by their cash flow situation."

She encourages her clients to start tracking both fixed and variable expenses, and sort out who will pay for what and when.

Opening a joint account can help you simplify paying bills like rent, insurance premiums and other fixed expenses.

"I do try to encourage that," Klingaman says. "Of course, keep your own accounts, but is there a way to streamline how you pay for things by opening up a joint checking account to pay for your fixed expenses together?"

2. Talk about what's 'yours, mine and ours'

There may be expenses you and your partner don't agree on — and that's OK. Especially if you have separate income streams.

Early in her own relationship, Klingaman and her husband ran into spending conflicts, which led them to create "yours, mine and ours" accounts. Instead of both contributing to and spending from a single shared checking account, they started putting some money into their own accounts for personal purchases.

"We had our joint spending account, which was for all things that we did together and shared expenses," Klingaman says. "But even that slight change — where I wasn't looking at the transactions that he's made that I didn't necessarily agree with — helped remove that disagreement and nagging from our conversations about money."

It's not about hiding your spending habits from your partner, but rather having your own space and funds to do the things that matter to you.

"There's got to be protection of our individual goals and values, and they're not always going to overlap with our partner's," Klingaman says.

3. Keep the conversation going

How you split costs might work now, but things can change in the future. When you first move in together you may split things down the middle by default, but as you go on, you may find a better system.

"Perhaps the couple works toward splitting things more proportionally as it becomes clear one person's income will be consistently different from the other's," Klingaman says.

It's OK if things change, as long as you're able to talk about it with your partner. "At that point, the couple has probably navigated a good number of money situations together, they've built up a healthy level of trust and understanding, and that has created common ground for handling money together more fairly."

Talking about money can be awkward or uncomfortable, even for couples who've been partnered for a long time. But it's important to be transparent and communicative about your finances, especially if you're sharing resources and relying on each other's incomes.

"I encourage couples to make sure they're having regular 'money dates' so that each person understands the other's money story," Klingaman says.

It's one thing to go over numbers and make sure there's enough income to cover your expenses as a couple. But Klingaman says it's helpful to understand where your partner is coming from and how they're making financial decisions so you can have more productive conversations and come up with solutions that make both parties comfortable.

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