Hello. My wife was paid as self-employed for the first three months of 2018 - her employer did not withhold federal taxes. She is now employed FT and her employer is withholding federal taxes. We want to make a quarterly payment for Q1 and I used TurboTax "Other Tax Issues" to make the calculations, but the amounts it's suggesting for quarterly payments seem too high. I used the estimated amount we will both make for 2018 as the AGI - was that correct? Or should I have only put in the amount my wife made as a contractor for the first three months of 2018? I feel like I must be doing something wrong or estimating incorrectly. The clock is ticking and I'm stumped! TYIA for any help!
In completing the 1040ES, did you include the amount of future withholdings as payments as well? Also, any withholdings from your earnings?
Using joint income is the proper way, as you want to estimate what the tax bill will be for your filing status, presumably married filing joint.
Also, you might consider increasing your wife's withholding from her paycheck. That might eliminate the need for 1040Es entirely, if enough withholding is made from all sources.