How early I can file my income tax return for the year 2019?

A 2019 tax return cannot be filed until after January 1, 2020.  However, as in past years the IRS probably will not be accepting any type of 2019 tax return until mid to late January.  So if you file earlier your return will just be sitting in queue waiting for the IRS to start accepting return. 

[Edited to correct year]

The IRS has not yet announced a date when they will start accepting 2019 tax returns. It will probably be mid to  late January. Keep in mind that you cannot file your tax return until you have all your W-2s, 1099s, and other tax documents. The issuers have until January 31 to send you those documents.