If your HDHP coverage changes from individual to family, or vice versa, during the year, your HSA contribution limit will be prorated based on the number of months you held each type of coverage.
To calculate your adjusted limit, use the “Limitation Chart and Worksheet” provided on IRS Form 8889. The worksheet helps you determine the appropriate contribution amount based on your coverage and eligibility throughout the year.
For more details, refer to IRS Publication 969 or consult a tax professional for assistance.
Source: "Publication 969 (2018), Health Savings Accounts and Other Tax-Favored Health Plans.”
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