1040es

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!