Property division is one of the most complex parts of a divorce. You have to completely separate your assets between you and your spouse in an agreeable way, which is not always an easy task.
If the court must assist with property division, it will do so based on state law, which is a fair division of property. The court will divide only those things that are marital assets.
According to Cornell Law School, marital property is that which you and your spouse obtained during the marriage. It could also include property that you had prior to the marriage that became marital property due to using marital assets to maintain it or some other situation in which you commingle the asset with marital property.
Separate property is anything you owned prior to your marriage. You must keep these assets separate. For example, if you owned a house but your and your spouse lived in that house during your marriage and you invested in the house during the marriage, then the appreciated value of the home is a marital asset.
There are some things that almost always remain separate. These include inheritances and gifts.
The categorizing of assets is not simple. As you can see, there are several exceptions and situations where property could become marital even when it started as separate or where something could be partially separate and marital. It is not an easy process to categorize and divide property, which is why it is usually best to try to work things out between you and your spouse rather than leaving it up to the court.