Do I need to pay the quarterly estimated tax payments in July, Sept and January 2020 if I change w4 allowances after making the 1st payment?

[mwaine]

By the end of the year, actually Jan 15, 2020, you must have paid 90% (this year only 80% by special exception which may not repeat) of the tax that will be due.  But if you've paid 100% of your 2018 tax bill as estimated taxes, you're safe no matter how much you'll end up owing in 2020.