The primary reason for making the quarterly estimated tax payments for 2019 would be to make sure you don’t incur a penalty for an underpayment of taxes when you prepare your return for 2019.
The easiest way to avoid a penalty is to make sure your 2019 withholding is equal to or greater than your total tax liability for 2018. This is referred to as the “safe harbor test.” Your total tax liability is the total taxes before accounting for withholding and estimated tax payments, not the amount that is due with your 2018 return.
However, if your taxable income for 2019 is going to be significantly less than it was in 2018 you may be better off just making sure your withholding exceeds your tax liability. This takes some planning and estimating of course. If you can accomplish this then you won’t incur an underpayment penalty.
So, depending on your situation you may not need to make any estimated tax payments.
I hope this helps.
Best regards.
Mike