I'm considering rolling a traditional IRA to a Roth, and I want to do an ESTIMATE of the tax impact. How do I fill out a fake 1099-R?

I'm considering rolling a traditional IRA to a Roth.  This is a complicated decision.  I ran TT 2017 and entered my best guess at what the number will look like.  Now I want to enter various rollover amounts and see what the tax impact will be.  But all I'm offered is a complicated "1099-R"!  What does that look like for an IRA to Roth rollover?