You should keep records of all HSA expenses for as long as your tax return is considered open and subject to an audit (typically three years), or as long as you maintain the HSA account, whichever is longer.
These records include any insurance carrier’s Explanation of Benefits (EOB) statement that documents the expenses for services covered under the High-Deductible Health Plan.
You should also keep receipts for items or services paid for with the HSA, for example, vision and dental services.
The IRS indicates that, in case of an audit, you should keep records sufficient to show the following:
The distributions were exclusively to pay or reimburse qualified medical expenses,
The qualified medical expenses had not been previously paid or reimbursed from another source, and
The medical expenses had not been taken as an itemized deduction in any year.1
1. “About Publication 969, Health Savings Accounts and Other Tax-Favored Health Plans.” Internal Revenue Service, May 1, 2020. https://www.irs.gov/forms-pubs/about-publication-969.