How to Fill Out Form 8889 Line 3 for Your HSA

Line 3 of Form 8889 is your personal HSA contribution ceiling for the year, and to fill it out you work through the month-by-month worksheet in the Form 8889 instructions: assign each month a dollar value based on your HDHP coverage type and eligibility on the first of that month, add the twelve amounts, and divide by twelve.¹ For 2026, the full-year numbers that feed the worksheet are $4,400 for self-only HDHP coverage and $8,750 for family coverage, plus a $1,000 catch-up if you’re 55 or older.² The reason Line 3 isn’t a single lookup is that your eligibility rarely lines up neatly with twelve months of unchanged coverage.

What Line 3 Represents

Line 3 sits in Part I of Form 8889. It is the maximum amount you’re allowed to contribute and deduct for the tax year, based on your specific eligibility months and coverage type.¹ It is not what you contributed. It is the cap your contributions will be measured against later in the form.

The 2026 Dollar Values You’ll Plug In

Before you can run the worksheet, you need the annual limit figures. For 2026:

Self-only HDHP coverage: $4,400 per year
Family HDHP coverage: $8,750 per year
Catch-up contribution if you’re 55 or older by December 31: additional $1,000

The base limits are adjusted annually for inflation. The $1,000 catch-up is fixed by statute and does not change.³

Your plan has to qualify as an HDHP for each month you count. For 2026, that means a deductible of at least $1,700 self-only or $3,400 family, with out-of-pocket maximums capped at $8,500 and $17,000 respectively (excluding premiums).²

Running the Monthly Worksheet

The Line 3 worksheet in the Form 8889 instructions evaluates each month separately. For every month, you answer three questions in order:¹

Were you enrolled in Medicare that month? If yes, that month gets $0.
Were you an eligible individual on the first day of the month? If no, that month gets $0.
What HDHP coverage did you have on the first of the month? Enter the matching annual limit: $4,400 for self-only or $8,750 for family. If you’ll be 55 or older by year-end, use $5,400 and $9,750 instead (the base plus catch-up).

Add the twelve monthly figures and divide by twelve. That quotient is your Line 3 amount. If you were eligible every month with the same coverage type, the arithmetic collapses: twelve identical values divided by twelve returns the full annual limit.

Prorating for Partial-Year Coverage

Eligibility is tested on the first day of each month. You only get credit for months when a qualifying HDHP was in place on that date and no disqualifying coverage applied.³ Months without HDHP coverage, or any month with Medicare enrollment, get $0.

Say you started family HDHP coverage on April 15, 2026. You weren’t covered on April 1, so April is a zero month. Your first eligible month is May. The worksheet gives you $8,750 for each month from May through December and $0 for January through April. The math: (8 × $8,750) ÷ 12 = $5,833. That’s Line 3, assuming no catch-up.

The common error here is treating your enrollment date as your start date. What matters is whether coverage existed on the first of the month, not when the policy was purchased.

The Last-Month Rule Shortcut

If you were an eligible individual on December 1 of the tax year, you can treat yourself as eligible for every month of the year and enter the full annual limit on Line 3.³ The late-year enrollee from the example above could use this rule and claim the full $8,750 instead of $5,833.

The cost is a testing period. You have to remain an eligible individual through December 31 of the following year. For HDHP coverage starting November 15, 2026 (first eligible date December 1, 2026), the testing period runs through December 31, 2027.³ If you fail it for any reason other than death or disability, the extra contributions you claimed get added back to gross income and hit with an additional 10% tax. If there’s any realistic chance you’ll move to a non-HDHP plan, pick up a general-purpose FSA, or enroll in Medicare during the testing year, the prorated calculation is safer.

Catch-Up Contributions at Age 55 and Older

If you’ll be 55 or older by December 31, the catch-up gets built into the monthly worksheet amounts rather than added at the end.³ Instead of $4,400 for a self-only month, you enter $5,400. Instead of $8,750 for a family month, you enter $9,750. The catch-up prorates the same way the base limit does: eight self-only months at $5,400 divided by twelve is $3,600.

Married couples should note that each spouse’s catch-up must go into that spouse’s own HSA. You can’t deposit both $1,000 catch-ups into one account. If only one spouse currently has an HSA, the other needs to open one to receive their catch-up.⁴ Each spouse files a separate Form 8889.¹

Switching Between Self-Only and Family Coverage

If your coverage type changed mid-year, the worksheet handles it month by month. Each month gets the limit matching the coverage you had on the first of that month. Family coverage January through June and self-only July through December produces six months at $8,750 and six at $4,400, totaling $78,900. Divide by twelve: $6,575.

There’s an additional rule when you were eligible all twelve months but changed coverage types. Line 3 is the greater of the worksheet result or the annual limit for whatever coverage you had on December 1.¹ In the example above, December 1 coverage was self-only ($4,400), less than the $6,575 worksheet result, so $6,575 stands. If you had instead switched from self-only to family mid-year and held family coverage on December 1, the $8,750 December figure could exceed the worksheet result and would become your Line 3.

Shortcut: if family coverage was in place on December 1 and you were eligible all year, you can skip the worksheet entirely and put $8,750 on Line 3.

Months You Must Zero Out

Having an HDHP isn’t enough on its own. Certain other coverage disqualifies you, and any month where it applied gets $0 in the worksheet, which pulls your Line 3 down.

General-purpose health FSA. If you or your spouse has one, you’re ineligible for HSA contributions for every month of that FSA’s plan year, even if the balance reaches zero mid-year.³ Limited-purpose FSAs restricted to dental and vision do not disqualify you.

Medicare. Enrollment in any part of Medicare, including premium-free Part A, ends eligibility. If you enroll after 65, Part A can be backdated up to six months, which may retroactively turn earlier contributions into excess contributions. People already receiving Social Security are auto-enrolled in Part A at 65.

VA medical services. Mere eligibility for VA care doesn’t disqualify you, but actually receiving non-preventive services at a VA facility blocks HSA eligibility for the three months following the visit. Care for a service-connected disability doesn’t trigger the block.³

Spouse’s non-HDHP coverage. If your spouse’s plan covers you and isn’t an HDHP, that counts as disqualifying coverage for you. Dental, vision, and accident-only plans are exceptions.

Checking Line 3 Against What You Actually Contributed

Once Line 3 is set, it becomes the ceiling that later lines in Part I measure against. Line 2 reports your direct contributions (from Form 5498-SA), and Line 9 captures employer contributions and pre-tax payroll deductions (W-2 Box 12, Code W).⁵ Line 13 produces the deduction that flows to Schedule 1.¹

The practical check: your personal contributions plus employer contributions can’t exceed Line 3. If they do, the overage is an excess contribution and faces a 6% excise tax for every year it stays in the account.⁶ You can avoid the excise tax by withdrawing the excess (and the earnings attributable to it) before your tax return’s due date including extensions; the earnings portion becomes taxable income in the year withdrawn.

Excess contributions show up most often when payroll deductions keep running at the family rate after a switch to self-only coverage, or when the Line 3 worksheet gets skipped and someone enters the full annual limit despite partial-year eligibility. Compare Box 12 Code W plus your direct deposits against your calculated Line 3 before filing. Contributions for the 2026 tax year can be made up until April 15, 2027, which gives you room to top up if your calculated Line 3 came in higher than you expected.⁴

1
Internal Revenue Service. Instructions for Form 8889 (2025)
2
Internal Revenue Service. Revenue Procedure 2025-19 – 2026 Inflation Adjusted Amounts for Health Savings Accounts
3
Office of the Law Revision Counsel. 26 USC 223 – Health Savings Accounts
4
Internal Revenue Service. Publication 969 (2025) – Health Savings Accounts and Other Tax-Favored Health Plans
5
Internal Revenue Service. Form W-2 Reporting of Employer-Sponsored Health Coverage
6
Office of the Law Revision Counsel. 26 USC 4973 – Tax on Excess Contributions to Certain Tax-Favored Accounts