Taxing. If one person pays more upfront than the other, Garrett says, couples can either agree to prorated ownership percentages or a schedule for the other person to catch up by paying the monthly mortgage bill. (Aside from the issue of fairness, Garrett adds, if one person provides the "gift" of a down payment, it may be subject to gift taxes.)
Differing monetary contributions underscore the need for a written agreement about what happens in the event of a dispute. "Sometimes people argue that they contributed more to a down payment. In some states, that may make a difference but not in others," says family law specialist Michele Lowenstein.
Parkinson's approach seems to have worked: When she and her boyfriend were ready to buy a bigger home six years ago, they made the offer and got engaged on the same day.