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Everyone’s heard the old adage about making assumptions – but when it comes to your money and your relationship, those assumptions can actually ruin relationships.

More than a quarter of those married or living with a partner say that disagreements over money are more likely to  cause arguments than disagreements about children, work, chores or friends, according to a 2012 study by the American Institute of Certified Public Accountants. Money differences among couples were also the strongest predictor of divorce, according to a 2012 Kansas State University Study.

Here are the seven deadly assumptions that many couples make:

1. My partner has everything under control

It’s perfectly fine for one partner to manage the finances, but both spouses should be aware of what’s going on and involved in financial decisions. Making a financial plan together (even if one person executes it) ensures that you’re on the same page about big decisions and eliminates surprises, which can lead to conflict down the road. “You have to learn to work as a team,” says Laura Knolle, a certified financial planner with Ballou Plum Wealth Advisors in California.

In addition, if the person who handles the finances ever becomes mentally or physically incapable of doing so, the other partner should be able to step in seamlessly and fill the role.

2. We’ve got the same money values

People have different priorities when it comes to budgeting, investing, and saving for the future. Rather than assume you’re on the same page, talk about your general money habits and your attitude toward risk. If your philosophies are far apart from your partner’s, talk about why you have the values that you do and look for a compromise that will suit you both. “Even if you have a lot in common and are in a loving relationship, don’t assume your partner has the same expectations towards money as you do. Talk about money openly and honestly,” says Anthony Criscuolo, a certified financial planner in Fort Lauderdale with Palisades Hudson Financial Group.

3. Combining our finances will be better for both of us

Combine finances or keep them separate? There’s no one solution that’s right for everyone. The most important thing is to discuss openly with your partner why you want to combine accounts – or keep them separate – so that you’re both in agreement as to which arrangement works best for you. Many couples have a hybrid plan with both individual and joint accounts. Whatever your choice, decide in advance how you’ll handle your regular income and expenses and whose accounts will be used, says Criscuolo.

4. It’s better if my partner doesn’t know about my purchase (or my debt)

Any purchase or financial decision that will have a significant impact on your finances as a couple should be discussed ahead of time. In particular, couples need to be honest about any debt they’re bringing to the relationship or any financial support they’re providing to family members.

Nearly half of couples have lied to a significant other about money matters, according to a 2012 study by Self.com and Today.com. Keeping secrets sends a message that you don’t trust your mate, and that’s an obvious recipe for relationship problems. Consider setting a spending threshold above which consent from both partners is needed before a purchase can be made.

5. We already had the ‘money talk'

Just because you’ve discussed your finances once doesn’t mean you’re finished. As your life changes, so, too, will your money strategies. Periodically revisiting your plans will ensure that neither of you has had a change of heart that could lead to resentment or misunderstandings if not addressed quickly. Gather your financial statements and bills, then schedule regular money “date nights” to review them together.

6. We’ll always be OK

You may have your financial house in order now, but proper financial planning requires looking ahead to the future to strategize for unexpected expenses or other financial issues. Spending without a safety net of savings could make the shock of an emergency such as a job loss or illness far more traumatic than if you were financially prepared. Choose to manage your money (rather than managing crises) by having an emergency savings account, a retirement savings plan, and other necessary protections such as life or disability insurance. “These are an important part of a financial plan and shouldn't be overlooked,” says Knolle.

7. I should keep my reservations to myself

Agreeing to everything just to avoid conflict is similar to being behind the wheel of a car that’s skidding on ice. “You are completely out of control and just waiting to run into something that brings you to a crashing stop. If you cannot say no, this not a good relationship in the first place,” advises Patrick Morris, CEO of Hagin Investment Management in New York City.

More than half of married consumers say their spouse has at least one bad financial habit, according to a survey last year by American Express. Whether it’s a large purchase decision, or the everyday spending habits of your partner, keeping mum is bad news for both of you. “Stop avoiding conflict. Just have it out,” Morris says. “Usually the fear of possible confrontation is worse than the actual confrontation.”

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