Citing "tactical reasons" for the delay, Biden said it is not his intention to stay in the country for a long time, per a Pentagon press release issued shortly after the first full news conference of his presidency.
He also said he "can't picture" having troops present in the country next year.
Biden made similar comments last week in an interview with ABC News.
The May 1 deadline was set in February of last year under then-President Donald Trump's administration, and in November then-Defense Secretary Christopher Miller announced plans to withdraw troops from Afghanistan by Jan. 15.
But this year's defense spending bill blocked funding for the drawdown until the Pentagon provided more information about how the change could affect U.S. security.
"What I will say is that it is obvious the level of violence remains pretty high in the country," Austin said. "We'd really like to see that violence come down. If it does not come down it can begin to set the condition for some really fruitful diplomatic work."
Secretary of State Antony Blinken was also set to return to the United States Thursday after two days of meetings with NATO allies to discuss the situation in Afghanistan.
Blinken said allies' views would be "an important factor" in determining the path forward.
Last week NATO Secretary-General Jens Stoltenberg said a united Afghan government is necessary to carry out intra-Afghan peace talks with the Taliban, and U.S. reconciliation envoy Zalmay Khalilzad called for a prisoner swap between the Kabul government and the Taliban.