The 2026 limit
The IRS sets one number a year, and for 2026 it is $4,400 for self-only coverage and $8,750 for family coverage, with an extra $1,000 catch-up from the year you turn 55. A family HDHP that covers two spouses who are both 55 or older carries two catch-ups, so its line is $10,750. Every dollar you deposit and every dollar an employer deposits counts toward that single line - the limit does not double because two parties are paying in, and it does not depend on whose name sits on the account.
What the limit caps is contributions for the calendar year, not the balance, so an account that has grown for a decade can be well past $4,400 and still accept this year deposits up to the limit. The page does not prorate: there is no mid-year start date, no change of coverage during the year, and no last-month rule. If any of those apply to you, the real figure will differ from the one printed here.
Room, and crossing it
Your own deposits are the monthly amount times twelve, and the planned total adds any employer deposit on top. Room is the limit minus that total, floored at zero so it never prints as a negative; the amount above the limit is reported separately as an excess, which is why a page showing $0 of room can still be telling you that you are over.
The excess is the expensive part. It is not deductible, it is taxed again when it comes out, and it draws a 6% excise tax for each year it stays in the account unless you withdraw it together with its earnings before the filing deadline. If the excess came from employer deposits, the fix runs through the employer (a payroll or W-2 correction), not an employee withdrawal. The monthly table makes the timing visible: the employer deposit is counted from January and room then falls by your monthly amount, stopping at $0 rather than going negative. With nothing planned at all, the page shows a warning instead of a total.
The tax saving
Only your own deposits reduce taxable income here, and only the part of them that actually fits. The deductible amount is the smaller of your own deposits and whatever the limit has left after the employer deposit - so if an employer puts in $5,000 against an $8,750 limit, at most $3,750 of your own money saves tax, whatever you contribute.
The saving is that deductible amount times your marginal rate, held between 0% and 100%. At 25%, $1,800 of deposits saves $450. Employer money adds no income-tax saving because it was never in your wages to begin with; it arrived already excluded. The number is income tax only, so it leaves out FICA, any state add-back, and the far larger benefit of tax-free withdrawals for qualified medical care later.
What decides the limit
The coverage tier does most of the work. If the high-deductible plan covers you and at least one other person - a spouse on the same plan counts - the family limit applies, no matter how many people are actually enrolled and no matter which of you owns the account. Age only adds the catch-up; it never changes the base limit or the family test.
Amounts below zero are treated as zero, so a negative monthly or employer figure cannot create room that does not exist. What the page cannot check is whether you are eligible at all: an HSA requires qualifying high-deductible coverage and no disqualifying coverage such as Medicare, and that is a fact about your situation rather than an input here. An estimate, not a return, and not tax advice.
The date the limit is measured against
The limit belongs to a calendar year, but the deposits that count against it can arrive after that year ends: a 2026 contribution can be made up to the 2027 filing deadline, so a household that notices unused room in March can still fill it. This page prices the year, not the calendar, and it does not ask when the money arrived.
That freedom has a price. A contribution made after the year closes is reported on the prior year form only if it was designated for that year, and a contribution designated for the wrong year quietly becomes an excess contribution for the year it landed in - taxed again and carrying the 6% excise tax until it is removed. The deadline is generous; the designation is not.
The counterexample: $4,400 of deposits in 2026 plus a $1,000 top-up in April 2027 designated for 2026 is a compliant year. The same $1,000 without the designation is a 2027 contribution, which puts 2027 over its limit by $1,000 and leaves 2026 with unused room - the same money, two outcomes, and the difference is paperwork.
Danfio