There are 3 ways you can avoid the penalty:
1. Pay 100% of 2018's tax liability
2. Pay 90% of 2019's tax liability.
3. Owe less than $1,000 total
If you owe the penalty, it is 0.5% of tax owed for each month late. This penalty is not that severe, dollar-wise, unless you grossly underpay.
