My wife works anywhere between 35 and 55 hours per week. I work between 25 and 65 hours. Plus, I published one book in November and have four more planned for this year, so no way of predicting online income.

TurboTax has another calculator. Theirs is supposed to show you options choosing between a bigger return and a bigger paycheck, but after filling in all the information it requested, the slider won't work in any browser, so I can only see what the refund would be with zero exemptions: $4000. I'd like some buffer against extra income but not quite that much. :)