Since you already completed the FAFSA for the school year, you wouldn't be able to submit another one (FAFSA will recognize you are using the same FAFSA ID and will direct you to the one you have previously submitted). In any case, you are to use the custodial parent when completing the FAFSA.
Per FAFSA:
If your parents are separated or divorced, the custodial parent is responsible for filling out the Free Application for Federal Student Aid (FAFSA). The custodial parent for federal student aid purposes is the parent with whom you lived the most during the past 12 months. (The twelve month period is the twelve month period ending on the FAFSA application date, not the previous calendar year.) Note that this is not necessarily the same as the parent who has legal custody. If you did not live with one parent more than the other, the parent who provided you with the most financial support during the past twelve months should fill out the FAFSA. This is probably the parent who claimed you as a dependent on their tax return. If you have not received any support from either parent during the past 12 months, use the most recent calendar year for which you received some support from a parent. These rules are based on section 475(f)(1) of the Higher Education Act of 1965 (20 USC 1087oo(f)(1)).
Biological parents who never married are treated the same as parents who are divorced.
Note, however, that any child support and/or alimony received from the non-custodial parent must be included on the FAFSA.
Please note that the discussion given above applies even if the parents each have equal 50% custody. The term "custodial parent" is not synonymous with custody. Usually the parent with whom the student lived the most during the past 12 months is sufficient, since there are an odd number of days in the year. However, in some cases a tie-breaker is needed, such as when the divorce was recent or when there are an even number of days in the year (e.g., a leap year). In such circumstances it is based on whichever parent provided more support. If that is not definitive, then the financial aid administrator at the college will make the decision, and this will usually be based on whichever parent has the greater income. (Some colleges will follow the logic in a multiple support agreement, but they are under no obligation to do so.)
Financial aid applications can be somewhat confusing because there are several different criteria applied for different kinds of parenthood:
1.The parent with whom the child lived the most during the past 12 months (the 12 months ending on the FAFSA application date).
2.The parent who provided more financial support to the child during the past 12 months.
3.The parent who provided the most financial support to the child during the most recent calendar year for which either parent provided more support to the child.
4.The parent who provided more than half the child's support (and will continue to do so).
5.The parent who has legal custody.
6.The parent who claimed the child as a dependent on their tax return.
7.The parent with the greater income.
As noted above, criteria 1, 2 and 3 are used for determining the custodial parent, with the first criteria being primary. In a situation where the parents split all costs equally (without even a penny difference), criterion number 7 is often used.
For determining household size (the number of family members), criteria 4 is the most important. However, the student's custodial parent gets to list him or her even if the custodial parent does not provide more than half of the student's support. This leads to the anomalous situation where a student can be counted as belonging to two different households. For example, suppose the non-custodial parent remarries and has college-aged children of his own. If the non-custodial parent provides more than half of the student's support, the non-custodial parent gets to list the student as a member of the non-custodial parent's household even though the custodial parent has also listed the student as a member of the custodial parent's household. (The IRS tax return instructions prevent this kind of double dipping on tax returns, but the FAFSA instructions apparently don't.)
Criteria 4 is also used to determine whether the student has one or more dependents, in the rules for specifying whether the student is an independent student with dependents.
Criteria 5 and 6 are not used in the financial aid formulas, but are sometimes used to give an indication of the right choice when the other criteria are insufficient. Criteria 6 is also sometimes used to substantiate claims made under criteria 4. For example, a financial aid administrator may ask a parent for a copy of their tax return, to see whether they claimed the child as a dependent. Criteria 6 usually implies criteria 4, because the IRS definition of a dependent includes a 50% support test. There IRS definition includes a few exceptions where the parent isn't required to provide more than half the child's support in order to claim the child as a dependent, but in almost every case, if the parent could not claim the child as a dependent (criteria 6), they did not provide more than half the child's support (criteria 4).