There are some general rules pertaining to timeliness of HSA account contributions. While employer contributions to an HSA don't have a particular “due date,” the employer should sufficiently follow the plan terms. So if an employer communicates to employees that employer contributions will be contributed at a specific interval (such as per pay period), the employer should contribute based on that timetable. As an outside compliance limit, the IRS generally allows employers to contribute to employees' HSAs through the tax filing deadline for the year in which the HSA contributions were due.
On the other hand, participant contributions withheld from employee paychecks, including employee-deferred HSA contributions, are subject to the DOL's plan asset regulations governing welfare and pension benefits. Specifically, participant contributions become plan assets "as of the earliest date on which such contributions can reasonably be segregated from the employer's general assets, but in no event later than 90 days after the payroll deduction is made." This generally means the outside limit for submitting contributions is 90 days, but this is not to be considered a safe harbor because contributions should nearly always be segregated in a matter of days rather than weeks.
This deadline applies to participant contributions coming into an employer's possession under the welfare benefit plan, including personal checks used to pay COBRA contributions, premiums during FMLA leave, retiree premiums, salary reductions under a cafeteria plan, and HSA contributions. As such, employers should contribute employee-deferred HSA contributions to their accounts as soon as the funds can be separated from the employer’s general account. In this way, the deadline for forwarding HSA contributions is similar to the deadline for forwarding employee 401(k) deferrals.
Keep in mind, though, that there is a safe harbor for small employers for this purpose. Employers with fewer than 100 participants can utilize a DOL "safe harbor" that gives them up to seven business days to deposit plan assets (including HSA contributions) to an employee's account.
When an employer has failed to forward participant contributions on a timely basis, there are procedures available to correct both the fiduciary breach and the prohibited transaction that has occurred. There is a DOL correction program available to employers that commit this failure. The Voluntary Fiduciary Correction Program (VFCP) allows employers to correct failures (such as failure to forward HSA contributions on a timely basis) by submitting an application for the program and filing a Form 5330, acknowledging the prohibited transaction. However, as with any compliance failure, an employer that fails to timely forward contributions should consult with legal counsel.
DOL information on the VFCP »