Is the HSA established the same date the HDHP is effective?

Not necessarily. While some employers ask individuals to establish their HSA the same date that their HDHP will be effective, this is not always the case. In order to establish an HSA, the individual must meet the eligibility requirements which include having no coverage by any non-HDHP health plan. So, if a person is covered by a health FSA or a spouse plan on the first day of the month their HDHP is effective, they would have to wait until the first of the month following the end of that coverage to establish their HSA. There could be other reasons that the individual delays establishing their HSA; however, all eligible individuals should be encouraged to establish their HSA since the IRS does not allow any expenses to be reimbursed prior to the HSA establishment date.