Facebook founder Mark Zuckerberg marked his return to work after a two-month paternity leave with a humorous post highlighting his utter lack of wardrobe choices.

"First day back after paternity leave. What should I wear?" the 31-year-old wrote on Tuesday (Jan 26).

The accompanying photo on Facebook revealed a row of identical grey T-shirts - his go-to outfit and something of a trademark Zuckerberg look - and navy blue sweaters in his closet.

In 2014, Mr Zuckerberg revealed during a public Q&A why he wore the same T-shirt every day, claiming that small decisions like what to wear or what to eat for breakfast could be tiring and energy consuming.

"I really want to clear my life to make it so that I have to make as few decisions as possible about anything except how to best serve this community," he said.

Mr Zuckerberg had taken a two-month break from work after his wife Priscilla Chan gave birth to their daughter Max in late November.

Full-time male and female Facebook employees are entitled to four months' parental leave.

Mr Zuckerberg celebrated Max's birth by announcing on Dec 1 last year that he and his wife would be giving away 99 per cent of their Facebook shares - worth about US$45 billion (S$64.4 billion) - to a new charity they had set up.

During his break, Mr Zuckerberg also posted several photos of Max, including her first swim and one of his five-year-old dog Beast posing next to her cot.