"I've never seen it said straight out. That is definitely new," said Washington area party planner Andre Wells.
The self-dubbed mom-in-chief turns 50 on January 17 and will hold her food-light celebration the next day, likely in the White House East Room.
There is no word on who is on the guest list, though many suspect hip-hop royalty Jay-Z and wife Beyonce will be among the revellers.
She got an early birthday present from the President - an extended Hawaiian vacation after the family holiday stay on the island.
The President and daughters Malia, 15, and Sasha, 12, returned to the arctic temperatures in Washington on Sunday, leaving the birthday girl behind.
The First Lady is relaxing at the Oprah Winfrey estate in Maui for a "girl getaway" with CBS morning host Gayle King, President Obama's adviser Valerie Jarrett and Sharon Malone, wife of Attorney General Eric Holder, The Daily Caller reported.
White House Press Secretary Jay Carney told reporters on Monday "the first family will appropriately fund personal expenses," but said a government aircraft will be used for her travel back to Washington.
