He will spend the morning working in the Oval Office before attending an afternoon party hosted by his staff. Obama and his family -- including First Lady Michelle, 47, and daughters Malia, 13, and Sasha, 10 -- will also attend a private party with friends Thursday evening.
On Wednesday, Obama treated his aides to pre-birthday burgers and fries on Capitol Hill. Shortly after, he flew to Chicago for a campaign fundraiser.
Later, at a private dinner, Obama made a few jokes about getting older. "By the time I wake up, I'll have an email from AARP asking me to call President Obama and tell him to protect Medicare," the President quipped. (Supporters paid up to $35,800 to attend the dinner.)
Obama didn't make it back to Washington D.C. until after midnight; he officially turned 50 while on Air Force One.