The custodial parent is the parent with whom the student lived the most during the past twelve months. The term "past twelve months" is relative to the date the FAFSA was submitted. It is not the previous calendar year.

If the student lived with neither parent or didn't live with one parent more than the other, the custodial parent is the parent who provided more financial support during the past twelve months, or during the most recent year during which the student received support from either parent.

It is not unusual for the parents to be living in the same house during a separation or after a divorce. Many financial aid administrators will require a copy of the divorce decree if the divorced parents are living at the same address.