Sold an attached lot to neighbor for a large gain from what it cost how would report on my 2024 return and fig. my basis. Would it only be what I actually paid for it?

Yes, the cost basis is what you paid for it. 

Thanks

And would it be excluded like sell all of your home, or part of it being excluded

Thanks

No. The exclusion is for the sale of your primary residence. 

Even though the lot was attached to personal residence nothing can be excluded?

No.  

@Then2 there is a special rule for certain vacant land. I don't know if it would apply in your situation

gain from sale of vacant land that has been used as part of the principal residence can qualify for the home sale exclusion if the land sale occurs within two years before or after the sale of the dwelling unit. Reg 1-121-1(b). The land must be adjacent to the land containing the dwelling unit, and all other requirements of 121must be satisfied. the sale of the land and the sale of the dwelling unit are treated as one sale for the exclusion limit.      

---

@Then2 wrote:

Even though the lot was attached to personal residence nothing can be excluded?

---

It's not clear if you are talking about a separate lot that was separate when you bought it, or you subdivided the lot that contains your primary home.

If you subdivided the lot that your main home sits on, you can exclude the gain as long as you also sell your home within 2 years.  And you just get one exclusion ($250,000 or $500,000 if filing jointly), you don't $250K on the lot and then another $250K on the primary home.  

If this was always a separate lot, then whether or not the exclusion is allowed depends on whether you used the land "as part of your main home."  If yes, then you can use the 2 year rule above.  However, if you treated the property as a separate lot not part of the main home, then an exclusion is not allowed.