We have a one person DB plan sponsor: FY is calendar. PYE is 9/30/18. He contributed for the 2017 plan year in Feb 2018 and filed his 2017 tax return without extension. Then he made the 2018 deposit in September 2018 before the 2017/2018 PYE. Since he deposited the money during the plan year it will be listed on the 2017 SB but he'll deduct it in 2018. The 2017 PY max deduction doesn't cover the entire amount, but we have room in and time to amend the formula back to 10/1/2017 so it is deductible. We are concerned with the deposits during being split between the 2 tax years. I think that it is ok but would like another opinion.