Answer:
Charles & Joan will be required to make estimated payments for 2016
Estimated payments to be made will be lower of the following
Estimated payments for the year 2016 is shown below
Taxable income for 2016 ($79,500 × $31,500) = $ 111,000
Tax @ 15% upto $75,300 = $8,512.50
Tax @ 25% ($111,000 - $75,300) = $8,925.00
Estimated 2016 tax liability $17,437.50
90% of estimated tax liability $15,694.00
It can be seen from above, that they have to pay $ 15,694 as it is lesser than $16,604
Tax withholding already done in 2016 = $11,594.00
Balance tax to be paid - Difference between the liability and withholding = $4,100.00
The additional tax to be paid is $ 4,100