If a married partner places a property that has been titled in her or his own separate name in the name of both parties, there is a presumption that the party transferring the property into joint tenancy intends to make a gift of one-half of the property to the spouse being added to the deed.
Even when the property is kept in the name of a spouse separately, however, unless there is a marital agreement to the contrary, the appreciation on the property is marital in nature. As an example, assume that a home worth $300,000 appreciates during a ten-year marriage to $400,000. The $100,000 increase in value is marital in nature, even though the original $300,000 in value is not marital.
Spouses who wish to keep property separate should consider having a marital agreement that spells out how they would like to have their property treated. If the agreement is entered into prior to the marriage of the parties, then it is a pre-nuptial agreement.