Yes, you can contribute the full family maximum for the year as long as both you and your spouse have coverage on December 1. The "full-contribution rule" (also known as the "last-month rule") allows individuals who are eligible on the first day of the last month of their tax-paying year (December 1 for most tax-payers) to be considered eligible for the entire year. Therefore, under these circumstances, you can contribute up to the full yearly maximum for your coverage type (self or family). In this case, an eligible individual is considered enrolled in the same HDHP coverage (i.e., self-only or family coverage) as he or she has previously been on the first day of the last month of the year. In short, if you have contributed the full amount this year for just yourself, you can increase that to the family maximum as long as your spouse has coverage on December 1. However, it is important to know that the IRS has a testing rule that applies for purposes of the full-contribution rule. Under the full-contribution rule, the testing period begins with the last month of your tax year and ends on the last day of the twelfth month following that month. For example, December 1, 2020, through December 31, 2021. If contributions were made to your HSA based on your eligibility for the entire year under the full-contribution rule, then you must remain an eligible individual during the entire testing period. If you fail to remain an eligible individual during the testing period (with the exception of death or disability), you must include the total number of contributions made to your HSA that would not have otherwise been made, apart from the full-contribution rule, as income. This amount must be included in your income in the year that you fail to be an eligible individual. This amount is also subject to an additional 10 percent tax. Income and additional tax are shown on IRS Form 8889, Part III.