Get your taxes done using TurboTax

Is it just the TaxCaster tool that says that, or is it the program itself?

Although 40% sounds quite high, MANY other things can change when you have more income.  Social Security Benefits may be taxable, many credits and deductions may be reduced or eliminated, your personal exemptions and itemized deductions may be phased out, and/or you may be subject to the 3.8% Net Investment Income Tax.