Q: My partner and I bought a duplex together and are 50/50 partners on everything dealing with the property, including renovations.

I currently live in the one bedroom unit downstairs. My partner has been living in the 2-bedroom upstairs with a roommate. The roommate pays $750 in rent each month. We’ve been putting the $750 toward the mortgage, taxes and insurance for the property and have split the remainder of the expenses equally.

There haven’t been any problems until now. The renter is moving out and my partner is moving his fiance in. How should we split our payments now?

A: You and your partner should have a written partnership arrangement that spells out your financial arrangement.

If you own the property 50/50, but he lives in the larger unit, then either you should change the ownership of the property to reflect that he occupies 66 percent of the home and you occupy 34 percent, or at least adjust the costs.

You and your partner should sit down and figure out what is equitable now that his living situation has changed. Perhaps he should pay 66 percent of the mortgage, taxes and insurance or perhaps you and he should talk to several local rental agents about how much each apartment unit would rent for. That could be the basis of your discussion. In some neighborhoods, a 2-bedroom unit would rent for more than twice as much as a one-bedroom apartment.

A real estate attorney can help you draw up the paperwork.