How to Fill Out Form 8889 Line 3 for Your HSA

Line 3 on Form 8889 is your maximum allowable HSA contribution for the tax year, calculated from your specific coverage months rather than pulled from a table. For 2026, the ceiling tops out at $4,400 for self-only HDHP coverage or $8,750 for family coverage, plus $1,000 if you’re 55 or older, but your Line 3 figure is often less because eligibility is measured month by month.¹ The number you enter drives everything downstream on the form, including your deduction and whether you’ve overcontributed.

What Line 3 Represents

Line 3 sits in Part I of Form 8889 and represents the cap on what you and your employer combined can put into your HSA for the year. It isn’t the amount you actually contributed. That number lives on Line 2. Line 3 is the ceiling those contributions are measured against, and later in Part I, Line 13 compares your actual contributions to this cap to produce your deduction.²

The IRS builds Line 3 through a worksheet in the Form 8889 instructions. Each month of the year gets a dollar value based on your coverage that month; the twelve values are added and divided by twelve. That average is Line 3.

The 2026 Numbers You’ll Plug In

Your health plan must qualify as an HDHP for each month you claim. For 2026, that means a minimum annual deductible of $1,700 for self-only or $3,400 for family coverage, with an out-of-pocket maximum no higher than $8,500 self-only or $17,000 family. Premiums don’t count toward the out-of-pocket cap.¹

For qualifying coverage, the 2026 annual limits are:

Self-only coverage: $4,400
Family coverage: $8,750
Catch-up contribution if you’re 55 or older by year-end: an extra $1,000

The base limits adjust for inflation each year. The $1,000 catch-up is fixed by statute and doesn’t change.³

Working Through the Month-by-Month Worksheet

For each of the twelve months, the worksheet asks three things in order:²

Were you enrolled in Medicare? If yes, enter $0.
Were you an eligible individual on the first day of the month? If no, enter $0.
What HDHP coverage did you have on the first of the month? Enter the annual limit for that coverage type: $4,400 self-only or $8,750 family. If you were 55 or older by year-end, use $5,400 or $9,750 to fold in the catch-up.

Add the twelve entries, divide by twelve, and that quotient is your Line 3. If you were eligible every month with the same coverage, the arithmetic collapses to the full annual limit.

Partial-Year Coverage and the First-of-the-Month Rule

Eligibility is tested on the first day of each month, not on any day you happen to be covered. A month only counts if you had qualifying HDHP coverage and no disqualifying coverage on that first day.³

Say you start family HDHP coverage on April 15, 2026. April doesn’t count, because you weren’t covered on April 1. Your first eligible month is May. The worksheet gets $8,750 for May through December and $0 for January through April. The math: (8 × $8,750) ÷ 12 = $5,833. That’s your Line 3 without catch-up.

This is the most common place people miscalculate. Your enrollment date isn’t the same as your first eligible month. What matters is what was true on the first.

The Last-Month Rule

If you’re an eligible individual on December 1 of the tax year, you can treat yourself as eligible for all twelve months and enter the full annual limit on Line 3. This is the last-month rule, and it’s a real benefit for anyone who picked up HDHP coverage late in the year.³

The cost is a testing period. You have to stay an eligible individual through December 31 of the following year. If HDHP coverage started November 15, 2026, making December 1 your first eligible date, the testing period runs from December 2026 through December 31, 2027.³

Failing the testing period is expensive. The extra you contributed beyond the prorated amount gets added back to your gross income the year you fail, plus a 10% additional tax on top. Only death or disability excuses you. If there’s any chance you’ll drop the HDHP, enroll in Medicare, or pick up a general-purpose FSA in the following year, prorate instead.

Coverage Type Changes and the December 1 Override

If your coverage changed between self-only and family during the year, the worksheet handles it month by month. Each month gets the annual limit tied to whatever coverage you had on that first day. Family coverage January through June, self-only July through December: six months at $8,750 and six at $4,400, summing to $78,900, divided by twelve, giving $6,575.

There’s a second rule for people eligible all twelve months whose coverage changed: Line 3 is the greater of the worksheet result or the annual limit for whatever coverage you had on December 1.² In the example above, December 1 coverage was self-only, and $4,400 is less than $6,575, so you’d use $6,575. Reverse the scenario, with family coverage on December 1, and the $8,750 December amount beats the worksheet, so $8,750 is Line 3. If family coverage was in place on December 1 and you were eligible the whole year, you can skip the worksheet and enter $8,750.

Catch-Up Contributions at Age 55

If you turn 55 by December 31, you can add $1,000 to your annual limit.³ The worksheet absorbs this by raising each monthly figure: $5,400 instead of $4,400 for self-only months, or $9,750 instead of $8,750 for family months. The catch-up prorates the same way as the base limit. Eight eligible self-only months at age 55 or older produces (8 × $5,400) ÷ 12 = $3,600.

Married couples run into a wrinkle. Each spouse who is 55 or older gets their own $1,000 catch-up, but it has to be deposited into that spouse’s own HSA. You can’t stack both catch-ups in a single account. If only one of you has an HSA today, the other spouse needs to open one to receive the catch-up.⁴ Each spouse files a separate Form 8889.²

Disqualifying Coverage That Zeroes Out Months

Having an HDHP doesn’t make you eligible on its own. Other coverage on the first of the month can knock a month down to $0 in the worksheet.

General-purpose FSA. A general-purpose health care FSA held by you or your spouse disqualifies you for every month of that FSA’s plan year, even if the balance runs out mid-year.³ A limited-purpose FSA that covers only dental and vision is fine.

Medicare. Enrollment in any part of Medicare, Part A included, ends HSA eligibility. Part A enrollment after age 65 typically backdates up to six months, which can retroactively convert contributions you already made into excess amounts. Stopping contributions at least six months before applying for Medicare avoids the problem. People collecting Social Security are automatically enrolled in Part A at 65, which catches some off guard.

VA medical services. Being eligible for VA care isn’t disqualifying by itself. Actually receiving non-preventive care at a VA facility blocks HSA eligibility for the three months that follow. Care for a service-connected disability doesn’t trigger the block.³

Spouse’s non-HDHP plan. If your spouse’s health plan covers you and isn’t an HDHP, that’s disqualifying coverage for you. Dental, vision, and accident-only plans don’t count.

Every disqualified month gets $0 in the worksheet, which drags Line 3 down accordingly.

From Line 3 to Your Actual Deduction

Once Line 3 is set, the rest of Part I turns it into a deduction:

Line 2 is your personal contributions for the year. Your custodian reports these on Form 5498-SA.⁵
Line 9 captures employer contributions, including pre-tax payroll deductions. This is your W-2 Box 12 Code W amount.⁶
Line 12 is Line 3 minus Line 9, which leaves the room still available for your personal deduction.
Line 13 is the smaller of Line 2 or Line 12, and it’s your HSA deduction. It flows to Schedule 1, Part II, line 13.²

Employer contributions already escaped tax through payroll, so only your personal contributions produce the above-the-line deduction. Because the deduction is above the line, you get it whether you itemize or take the standard deduction. You have until April 15, 2027 to make contributions for the 2026 tax year.⁴ Contributions posted between January 1 and April 15, 2027 can be assigned to either 2026 or 2027, but not both.

When Line 3 Is Wrong: Excess Contributions

If total contributions (yours plus your employer’s) exceed Line 3, the overage is an excess contribution and carries a 6% excise tax for every year it sits in the account.⁷ You can avoid the excise tax by withdrawing the excess and its earnings before your return’s due date, including extensions. The earnings become taxable income for the year of withdrawal, but the recurring 6% goes away.

Mid-year coverage changes are a common trigger. Switch from family to self-only and leave payroll deductions on the family schedule, and you can blow past your limit in a handful of paychecks. Cross-check your Box 12 Code W against your Line 3 calculation before filing.

1
Internal Revenue Service. Revenue Procedure 2025-19 – 2026 Inflation Adjusted Amounts for Health Savings Accounts
2
Internal Revenue Service. Instructions for Form 8889 (2025)
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 5498-SA – HSA, Archer MSA, or Medicare Advantage MSA Information
6
Internal Revenue Service. Form W-2 Reporting of Employer-Sponsored Health Coverage
7
Office of the Law Revision Counsel. 26 USC 4973 – Tax on Excess Contributions to Certain Tax-Favored Accounts