He signed the bill at about 3:30 p.m. on Tuesday.
The National Assembly had on December 5, 2019, passed the budget estimates presented by Mr Buhari on October 8, 2019.
The National Assembly increased the budget estimates from N10.33 trillion to N10.50 trillion.
The passage was a sequel to the presentation of a report by the chairman of the Senate Committee on Appropriation, Barau Jibrin.
The signing was witnessed by Vice President Yemi Osinbajo, President of the Senate, Ahmed Lawan and Speaker of the House of Representatives, Femi Gbajabiamila.