Prorated limits by months eligible (2027)
| Months eligible | Starts | Self-only | Family |
|---|---|---|---|
| 12 | Jan 1 | $4,500 | $9,000 |
| 11 | Feb 1 | $4,125 | $8,250 |
| 10 | Mar 1 | $3,750 | $7,500 |
| 9 | Apr 1 | $3,375 | $6,750 |
| 8 | May 1 | $3,000 | $6,000 |
| 7 | Jun 1 | $2,625 | $5,250 |
| 6 | Jul 1 | $2,250 | $4,500 |
| 5 | Aug 1 | $1,875 | $3,750 |
| 4 | Sep 1 | $1,500 | $3,000 |
| 3 | Oct 1 | $1,125 | $2,250 |
| 2 | Nov 1 | $750 | $1,500 |
| 1 | Dec 1 | $375 | $750 |
A month counts if you are eligible on its first day. Add $1,000 (also prorated) for age 55+.
The last-month rule, step by step
- You have HSA-eligible HDHP coverage on December 1, 2027, and no disqualifying coverage.
- You are treated as eligible all year, so the limit is the full $4,500 or $9,000 (based on your coverage on December 1).
- You then have a testing period from December 1, 2027 through December 31, 2028 and must stay HSA-eligible.
- If you stop being eligible during the testing period (for example, you leave the HDHP), the extra amount beyond the prorated limit is added to your income and generally carries an additional 10% tax. Death and disability are exceptions.
Worked example: new job in July
| Question | Answer |
|---|---|
| Self-only HDHP starts | July 1, 2027 (6 months) |
| Prorated limit | $2,250 |
| Full limit under the last-month rule | $4,500 |
| Extra room from the rule | $2,250 |
| Employer deposit of $400 | Your room: $4,100 with the rule, $1,850 without |
If the same person later switched to a non-HDHP plan in March 2028, the $2,250 of extra room would generally become taxable income plus the 10% additional tax. Switching between self-only and family coverage works month by month, and the last-month rule uses the coverage you have on December 1. Contributions from a prior employer and from you both count toward one limit.
Sources: IRS Publication 969 (last-month rule and testing period); IRS Form 8889 instructions. Checked October 18, 2026.
Related: family vs self-only · married couples · 2027 limits hub.
This is general information, not tax or insurance advice. Confirm details with your plan documents, the IRS and a qualified professional.
General education, not insurance, tax or legal advice. Figures from IRS and HHS publications; confirm with your plan documents.