Why was my federal taxes accepted on January 18th?

If your federal return was accepted on January 18, you were one of a small number of taxpayers selected for the IRS test batch.

E-file was opened this year on January 29, so if you return was accepted before that date, you were processed in the test batch.

This is a random selection that happens every year. 

So does that mean I should count the 21 days from the 18th or still go by the 29th?

You could count the 21 days from 1/18/2024, when your Efile was Accepted.

However, it's best to check the IRS Where's My Refund? link for current refund status.