The penalty for filing between one day and one month late is 5% of the amount you owed. Then, there is interest on the tax plus the penalty at about a 4% APR. The IRS will send you a bill. If you have never owed a penalty before, you can request a one-time penalty abatement. You would apply for the abatement after you get the penalty bill.
https://www.irs.gov/businesses/small-businesses-self-employed/penalty-relief-due-to-first-time-penal...
