I purchased real estate in 2018 and did not enter this information when filing. Should I try to enter that now or do I need to inform only after I sell?

[SweetieJean]

A personal home? Rental property? Investment land?

[markjernigan]

Investment land, possibly to build my own house to live in.

[markjernigan]

Investment land, possibly to build my own house to live in.

[markjernigan]

It is a city lot.

[Hal_Al · Accepted solution]

The actual purchase of the property is not entered anywhere on your tax return.

If you itemize deductions, you may deduct the real estate tax paid, including the tax paid at closing.

Since it is not really a 2nd home, yet, you cannot deduct mortgage interest.

Mortgage interest is only deductible, as an investment expense,  to the extent of other investment income, 

[Hal_Al]

Until you put it to use as your primary or second home or as rental property, or sell it, you have an investment property. The carrying costs (e.g. insurance & utilities) of investment property are no longer deductible as investment expenses, under the new tax law. But, real estate (property) tax may be deducted on schedule  A.

Taxpayers can elect to capitalize (add it to your cost basis)  the carrying costs of unimproved and nonproductive real property, real property under development or construction and personal property before its installation or use (Regs. Sec. 1.266-1(b)(1)).  The election is made with the tax return by its due date, including extension, by attaching a statement. You cannot wait until you sell the property, but must make that election each year. Attach the statement to the return and write “Filed pursuant to section 301.9100-2” on the statement.
Mortgage interest is only deductible to the extent of other investment income,  but can be capitalized.

[SweetieJean]

Well, you get to deduct any property taxes that you paid on it.