U.S. Senate Runoff Elections, Explained

In nearly every state, a U.S. Senate candidate wins by getting more votes than anyone else — a plurality. A three-way race can be won with 40% of the vote if that's the largest share. Georgia and Mississippi work differently: their state law requires the winner to clear an outright majority, more than 50% of the vote. When two major-party candidates plus one or more minor-party or independent candidates split the vote and nobody reaches that bar, the top two finishers face each other again in a runoff a few weeks later.

The runoff campaign is compressed. Georgia's runoff window is four weeks after the general election — cut down from nine weeks by a 2021 state law, SB 202, which also reduced early voting in runoffs from three weeks to one. That's a much shorter runway than a normal general-election campaign, and it changes the race: less time for outside money to move in, less time for early and mail voting, and a turnout pool that tends to be older and more habitual than the November electorate.

Turnout typically drops from the November baseline but not by as much as intuition suggests. In Georgia's December 2022 Senate runoff, roughly 3.5 million people voted — about 90% of the nearly 3.9 million who voted in the preceding November general, and far higher than the roughly 57% turnout ratio in Georgia's Senate runoffs of 1982 and 2008.

In the January 5, 2021 double runoff, Democrat Jon Ossoff defeated incumbent Republican David Perdue by about 1.2 points, and Democrat Raphael Warnock defeated incumbent Republican Kelly Loeffler by about 2 points. Both races had gone to a runoff because no candidate reached a majority in November 2020. The two Democratic wins flipped the Senate to an even 50–50 split, with Vice President-elect Kamala Harris's tie-breaking vote handing Democrats control of the chamber for the 117th Congress.

Two years later, Senate control wasn't on the line the same way — Democrats had already secured 50 seats — but the December 6, 2022 runoff between Sen. Warnock and Republican Herschel Walker still mattered: Warnock's win gave Democrats an outright 51–49 majority, ending their reliance on the vice president to break ties for the rest of that Congress.

Georgia's 2026 Senate race — incumbent Democrat Jon Ossoff against Republican Mike Collins — is rated a genuine toss-up. If national results leave the Senate close and neither Georgia candidate reaches a majority on November 3, the December 1 runoff could once again be the race that decides which party controls the chamber for the 121st Congress — right as the rest of the country's election coverage is winding down.