While this doesn’t give too much to go on, they key word in 26 U.S.C. 7201 is willfully. Accidentally underreporting income or incorrectly calculating a deduction is not a criminal offense (although it could still trigger an IRS audit or investigation). However, IRS investigators and Department of Justice (DOJ) prosecutors can infer willfulness from a variety of circumstances. Even if you did not set out to defraud the IRS, this does not necessarily mean that you are immune from criminal prosecution.