If both partners own homes, they need to decide where to live. They might choose to buy a house together, or have one spouse move in with the other.

Montanaro says one key question must be answered: "If I sell my house and move in with you, what happens if you pass away (first)?"

Where to live is just one of the details involved in merging into marriage. Some couples may decide to keep their finances separate, or set up a joint account to pay household expenses.

Others may divvy up costs depending on each spouse's resources and interests. A husband who doesn't golf, for instance, may not feel like splitting country club dues with a wife who hits the links regularly. "Not everyone is created financially equal," Montanaro says.

The bottom line: Matrimony will be happier if a couple has a budget that "makes sense for them, based on the lifestyle they want," says Debra G. Speyer, a Philadelphia attorney.