Other than TaxCaster (at the link SJ posted)
....and also as SJ noted.....Anyone who uses the download/desktop version of TurboTax has access to a "What-If" worksheet that uses that year's information, and allows you to change those values to what you expect for the next year.....and then it uses the known next year tax rates to predict the outcome. All of that without screwing up your current tax return. It is only for Federal tax returns (I don't foresee it ever being available for the states)
Married couples can also use the "What-If" worksheet to compare Federal MFJ vs MFS for the rare situations where that might need to be checked.
Maybe...someday they'll have that for Online software user's too, but don't hold your breath.
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