Critter-3 is exactly correct IMO. Both incomes need to be entered and I personally recommend withholding at a slightly higher rate for that miserable write-them-a-check experience when filing your taxes. That said, you can manage your withholding relative to what you are likely to owe -- usually it's as simple as tracking YTD withholding on your pay records issued by employers. Toward the end of the year if it looks like you are going to either owe or get a higher than anticipated refund, adjust your withholding in October or so for earnings through the end of that year. Then take what you learn into the next year and apply that withholding rate / amount / category and simply make adjustments for whatever increases in income you have proportionately / by percentages. It may sound complicated but it really is easy / straightforward. And unfortunately it is necessary in the situation we all live in today with America's tax system. Tools may get you into the ballpark, but if you want it to work out well you essentially have to manage it yourself actively. Anyone that tells you differently is.... Well, let's simply say they don't have to live with the outcome like you do! Hope this is helpful.
