5330 question on late deposits

Plan had amount involved of $400, so tax is $60 for late deposits in 2024.

Amount was corrected in 2025.

We prepared the 2024 5330 for $400/60

Since it was corrected in 2025, we are preparing a 2025 form as well.  My admin group wants to put $800/120 on the form because it extended two years.  is that right?  Do they have to pay $60 tax for 2024 AND 2025?  Seems to me like a 100% penalty for not paying the tax right away.

Yes, it sucks not catching and fixing it by December 31 of the same year.  The original PT was over two tax years.  The new 1-1-25 PT only gets multiplied by the 15% once.

Right now, we have two 5330's.  

2024:  $400 involved, $60 due

2025: $400 involved, $60 due for 2024 and $400 involved and $60 due due to carryover for 2024

(So if you add them up, it's $180 due!)

Also, it seems as though the 2024 form is now late and subject to penalties.  Do we have leeway to ask for abatement since the error was not caught until 2025?

For 2024, the amount involved was ($400 so 15% tax of $60) was due by 7/31/2025.

For 2025, the amount involved is the ($400 plus $60 for the unpaid tax for 2024, i.e., $460 * 15% = $69), and is due by 7/31/2026.

For 2026, the amount involved is ($400 plus $60 for the unpaid tax for 2024 plus $69 for the unpaid tax for 2025) * 15% = $79.35 that can be prorated on the number of days in 2026 the tax was unpaid.  If it is paid now, this would be 1/2 of $79.35 = $39.68.

The total taxes are $60 + $69 + $39.68 = $168.68.

Note that on the 5330 you can report all of the taxes due that are subject to the same tax rate regardless of the tax year.

This is all spelled out (somewhat opaquely) in Revenue Ruling 2006-38.

Double check the math on any of the above before filing the taxes.

Do submit a cover letter requesting an abatement of any interest and penalties.  Otherwise, the IRS may feel obligated to bill interest and penalties after reviewing the form.

Note that at least a couple of software/plan document vendors now offer a 5330 filing service that make this process much easier.

Isn't the 2025 tax due by the date they file their taxes?

The 5330 has its own deadline.