There is no deadline. The IRS has confirmed you can reimburse a qualified expense any number of years later, as long as you kept the records.
There is no time limit. This is the single most important rule in HSA planning and the one most people never hear.
IRS Notice 2004-50, Q&A-39 addresses it directly: a distribution can reimburse a qualified medical expense incurred in any prior year, provided the expense was incurred after the HSA was established and has not been reimbursed or deducted elsewhere.
Three conditions have to hold:
Nothing about the year. A 2026 receipt is as reimbursable in 2050 as it is next Tuesday.
The practical constraint isn't the tax code — it's whether the paper still exists. That's the whole reason this product does what it does.