In Georgia, a candidate must get at least 50% of the vote to win an election. In cases where no candidate gets 50% because of write-ins or multiple candidates, the leading two candidates must compete in a runoff election.
Georgia’s Senate runoffs are Jan. 5, with early voting starting Dec. 14. Dec. 7 is the deadline to register - and if you'll be 18 by Jan. 5, you're eligible. There are State and local runoffs on Dec 1.