Gain on excess annual additions

[Guest ktyler]

How do you calculate gain on excess annual additions? Is it only for the plan year for which the excess amount was contributed, or does gap gain also apply?

[Blinky the 3-eyed Fish]

There are no set rules to my knowledge, only to do something reasonable. I have always just applied the same safe harbor rules that apply to excess contributions figuring those can't be considered unreasonable.