Wow!!!! 

I leave my computer for a few hours and miss so much.  First of all, thank you everyone for taking the time to respond to my question.  Based on all these responses I guess I'm still a bit confused.  

To be clear, the property was transferred by a gift from my clients parents to my client.  Let's call my client John.  I am unaware if John's parents filed a gift tax return  as I do not prepare John's parents taxes.  I have asked John if his parent's filed a gift tax return and I am waiting for that answer.  

To simplify things I am going to outline this fundamentally.   John's parents purchased the home over 30 years ago and owned the home outright at the time of transfer/gift to John.  John's parents purchased said home for $80,000 and paid off the mortgage long before transfer.  John is unable to locate any documentation on this but is still searching  No significant improvements (replacement of roof, new driveway, new A/C) were made to the home in the last 12 months prior to transfer, so I'm assuming the donors original basis is $80,000.

Parent's gifted home to John in December 2023.  Again, I am uncertain if a gift tax return was filed/paid (I've asked John to provide me this documentation).

I've asked John for the appraisal as an appraisal was done around the time of the transfer/gift to John.  John believes the appraisal amount to $380,000 but will firming this up by providing appraisal.   Based on this, I am assuming the FMV of the home at the time of transfer is $380,000.

John sold the home in February 2024 for $400,000 and purchased a new home in April 2024 for $500,000.  The purchase of the new home is irrelevant however as the tax laws have changed with respect to reinvesting the gain into a principal residence to defer the gain.

As John did not own or live in the home for a 24 month period it appears that John is ineligible for the exclusion of the gain.  That said, I am now trying to determine the amount of the gain that John will have to pay taxes on.  The answer to this question is significant so I want to be double sure I understand how to calculate this. 

So here's the question:

Is Johns Basis in the home he sold the FMV of the home at the time of transfer ($380,000) or is John's Basis in the home the donors (John's parents) original basis ($80,000)?

I've read and re-read Publication 551 Basis of Assets (12-2024).  The publication states that "if the FMV of the property equal to or greater than the original adjusted basis , your basis is the donor's adjusted basis at the time you received the gift."  

So what is John's basis in the Property?  FMV or Donor's original basis?