Mega Back Door Roth

Where can I find out more about Mega Backdoor Roth

I'd just google it - there's been a lot of press about it. Biggest thing (IMHO) to watch out for is that it is subject to ACP testing, so often doesn't work in small plans, since generally utilized only by HCE's...

Also, people often miss that the after-tax money has to be deposited within 30 days after the end of the plan year to count for 415 limits.

Correct - only works in HCE-only plans or very large plans that can also pass ACP testing because of generous match and excellent NHCE participation. Need to make sure that VAT contributions are tracked separately and get converted before any investment earnings accrue or pick up any such earnings as taxable upon conversion. This can be done via in-plan conversation or withdrawal of the VAT account, just make sure you have provider that can accommodate and all is properly tracked and reported.

4 hours ago, Bill Presson said:

Also, people often miss that the after-tax money has to be deposited within 30 days after the end of the plan year to count for 415 limits.

that applies for sole-props as well and many (if not majority) of CPAs think it is OK to deposits VATs by September-ish.