How much taxes can I owe to not avoid underpayment penalty, and I will just pay it off later with credit card by tax deadline?

[SteamTrain]

1)   Simple answer:  If you owe less than $1000 for Federal is OK all of the time as long as all your payments during the year were from withholding, and no quarterly tax payments were involved...... state $ limit amounts vary.

2)  More complex:   In general....If you owe more than $1000 to Feds, and only had tax withholding, then it depends on whether your withholding was greater than last year, what your tax liability is for 2018 (before considering withholding),  and what your tax liability was last year.

3) More More complex:  a) If you had both withholding  (or no withholding) , but also made 4 exactly equal quarterly tax payments (on time) during the year, then the less than $1000 balance due at tax time applies. b) If you had both withholding  (or no withholding) , and made uneven quarterly tax payemnts...or didn't make all of the 4 quarterly tax payments, then it gets really messy, and you could owe an underpayment penalty even if you are due a refund

[Opus 17]

For most taxpayers, you will not owe a penalty if the amount you owe when you file your tax return is less than $1000; or the amount you paid into the system through withholding and estimated payments is greater than 90% of what you end up owing; or the amount you paid into the system is at least 100% of your tax liability from last year.