Send in the form as soon as possible after October 1. Do not wait until your taxes are done. Although it is better to do your taxes early, it is ok to use estimates of your income, so long as they aren't very far off from the actual values. You will have an opportunity to correct any errors later. If you wait too long, you might miss the deadline for state aid. Most states require the FAFSA to be submitted by March 1, and some even as early as early or mid-February.