I will have a remaining 2018 tax liability. I have already paid much more than my 2017 tax. Do I have to pay a quarterly tax in January, or can I wait until April?

[TomYoung]

IF you are saying, "I've paid more in taxes than (for most people) the tax shown on line 63 of my 2017 income tax return", THEN you've probably paid enough in taxes to not be "underpaid" when you file your 2018 income tax return and pay the tax due.

The word "probably" is in that sentence because the "safe harbor" you're trying to get into is this one:

"You may avoid a penalty for underpayment of estimated taxes if you pay at least 90 percent of your total tax on this year’s return (2018 return) or at least 100 percent of the total tax shown on last year’s return (2017 return). If your adjusted gross income for 2017 was more than $150,000 ($75,000 if your 2018 filing status is married filing a separate return), substitute 110 percent for 100 percent."

Details matter in these things and no one here knows those details.

Tom Young