Must an extra pymt to my 2018 HSA be done through an extra payroll deduction or can it be a deposit with after tax dollars from an existing checking or savings account?

[regenaom]

We did not make the maximum contributions in 2018 and both of us qualify with high deductible plans.

[Opus 17 · Accepted solution]

You can only do it by sending money to the HSA bank, any payroll contributions will automatically be recorded as for this year.  And when you send the money, you will need to make sure it is recorded as for the past year.  This may require a special form or menu selection on-line.