The October SAT is extremely popular among seniors since scores arrive in time for nearly all application deadlines. If you're hoping to take the October 5th test, you need to act today. The regular registration deadline has come and gone, but you can register late online up through the end of today, Monday, September 23th. Just go to the College Board's SAT Registration webpage to sign up. Note that you'll need to pay at $27.50 late fee on top of the regular $51 exam fee.