Planning is the best!
We have several tax calculators on our website for forecasting just that thing. It also depends on how granular you want to go.
There are a couple of other options. If you have TurboTax Desktop, there is a "what-if-worksheet" that easily lets you play that game. Or you can set up a dummy TurboTax Online account and model. Since forms aren't final, it's all an estimate. But, these choices should get you better handle on the tax situation.