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☑ ☐ UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - Q QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31 , 2021 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number 001-38139 BY Byline Bancorp , Inc. Byline Bancorp , Inc. ( Exact Name of Registrant as Specified in Its Charter ) TM Delaware ( State or Other Jurisdiction of Incorporation or Organization ) 180 North LaSalle Street , Suite 300 Chicago , Illinois 60601 ( Address of Principal Executive Offices ) ( 773 ) 244-7000 ( Registrant's telephone number , including area code ) 36-3012593 ( IRS Employer Identification Number ) Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No ☐ Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( $ 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No □ Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer " , " accelerated filer ” , “ smaller reporting company " , and " emerging growth company ” in Rule 12b - 2 of the Securities Exchange Act of 1934 . Large accelerated filer Non - accelerated filer Accelerated filer Smaller reporting company Emerging growth company ☑ ☐ ☑ If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . Yes No Securities registered pursuant to Section 12 ( b ) of the Act : Title of each class Common Stock Trading Symbol Name of each exchange on which registered New York Stock Exchange BY Indicate the number of shares outstanding of each of the issuer's classes of common stock , as of the latest practicable date : Common Stock , $ 0.01 par value , 38,629,513 shares outstanding as of May 5 , 2021