did you mail your return? did you have a balance due? if so, when was it paid payment was due on or before 4/15/19)? if not, did you later get a notice saying the iRS changed your return and you now owe.
put another way, even on a timely filed return, a late payment penalty arises when you owe on the return but don't pay by the due date. if you did pay timely, you can contest the penalty by sending back the notice and including proof that the payment was timely. this can be a copy of the cancelled check or if you did direct debit a copy of bank statement or credit card statement.
Even if you paid on time by April 15,
If you do not pay enough tax, you may have to pay a penalty for underpayment of estimated tax. Even if you are getting a refund you can still owe a penalty for not paying in evenly during the year.
Did Turbo Tax calculate an estimated penalty?
The amount Turbo Tax calculates on your return 1040 line 23 is only an estimate. Turbo Tax can not figure it accurately because they don't know exactly when the IRS or state will get your return and tax due payment. It's very common and normal and expected for the IRS or state to bill you for more or send you a refund.
IRS info on Underpayment Penalties..