@louvallee - the credit doesn't expire....you can keep rolling it forward indefinately if you are unable to use it all. Look at Line 18 of form 1040. The credit can reduce the tax on that line, but can't go below zero. The part that is left over is the rollover.
So if the credit < Line 18, there is no rollover as you will use it all.
if the credit > Line 18, the difference is the rollover.
