"Not Today" received generally positive reviews from music critics. Rhian Daly of
NME listed it as one of the best songs of BTS and praised the track's lyrical content stating that it is "a fiery, fierce track on which they encourage their fans to live their best lives." Sungmi Ahn from
The Korea Herald acclaimed the song for staying "true to BTS’ hip-hop driven roots" which she felt "is what the band excels at." She further deemed the track as "exhilarating" and added that it "pumps up listeners." Writing for
Billboard, Monique Melendez praised the song's message and sound labelling it as "equal parts social commentary and floor-shaking thrills." For
Digital Music News, Paul Resnikoff called the track "high energy" and "explosive" with "an elaborate dance and multiple backdrops." Allison Franks from
Consequence of Sound enjoyed the track and deemed it as an "explosive rap-based anthem", while Markos Papadatos of
Digital Journal regarded it as an "upbeat and spitfire" single. "Not Today" debuted and peaked at number six on the
Gaon Digital Chart for the chart issue dated February 12–18, 2017. "Not Today" was the 32nd-best-performing song of the February 2017 issue of the
Gaon Monthly Digital Chart based on digital sales, streaming, and background music (instrumental track) downloads. As of December 2017, it has sold 258,206 digital units in the country. The song debuted at number two on the US
Billboard World Digital Songs Chart for the issue date of March 4, 2017, selling 12,000 digital downloads in its first week. The following week, it climbed to the top spot, giving BTS their fourth number one on the chart following "Fire", "Blood Sweat & Tears" and "Spring Day". Additionally, it peaked at number 23 on the
Billboard Japan Hot 100, and number 77 on the
Canadian Hot 100. ==Music video==