<prompt> Human: For example, if you setup an HSA through your company and the account opened up in December 2017, could you still contribute the maximum limit for the year immediately? I believe so, but wanted to confirm.  <response>: As long as you are eligible on December 1st of a year you can contribute up to the maximum allowed for the entire year, but you must maintain eligibility for the HSA through December 1st of the following year.Its called the last month rule, if you want to look it up in more detail.The deadline for prior-year contributions is the tax filing deadline for that year. 