You are correct, egg donation is considered one-time income. There was actually a US Tax Court case about this in 2015, and the IRS held that payments for fertility egg donations are considered taxable income. This is the issue. Take a look at your 1099 and double check your entries in TurboTax. If there is no withholding (the box is blank) then it means that you haven't paid tax on the income. When withholding isn't taken from taxable income, the IRS will collect the tax owed after you file your tax return for the year. That is what is causing the software to calculate tax owed.
