You may contribute to an HSA up to the return due date of April 15th (no extensions). Please keep in mind that you must qualify to contribute  to an HSA

 To be eligible, a participant must meet the following requirements. 

Must be covered under a high deductible health plan (HDHP). • 

Cannot have any other health coverage.

 Exception: Coverage for specific things such as disability, dental care, vision care, and long-term care can be purchased in addition to the HDHP without disqualifying the HSA. • 

Cannot be enrolled in Medicare. • 

Cannot be eligible to be claimed as a dependent on someone else’s tax return.