There's nothing magical about the name "museum" in tax law. A museum that can't accept tax-deductible contributions can't give you a write off. Museums that qualify usually are set up as a not-for-profit foundation. Usually a museum will advertise the tax break if it's available, but you can also look up a particular museum online. The IRS maintains a charity-finder web page that tells you whether a particular museum, or any charitable group, qualifies.
The IRS says that if your membership gives you special benefits, you subtract the value of those benefits from the value of your donation. This doesn't apply if all you get as a member is unlimited museum visits, or something trivial such as a car decal. A free $100 ticket to an exclusive museum event would be another matter. If your membership costs more than $75, the museum has to tell you in writing the value of any benefits that eat into your potential deduction.
Taking the Write-Off
You can write off your museum membership only if you itemize. If you take the standard deduction, you can't claim your membership costs. Add together all charitable donations to qualified organizations to get your total write-off. If your total contributions for the year are greater than 20 percent of your adjusted gross income, IRS Publication 526 lists various restrictions on the amount of your deduction. If you buy a multi-year membership, you claim all of it as a deduction the year you wrote the check.
If you're ever audited, the IRS may ask for proof you made the donations you claimed. The auditor will want to know the name of the agency, the amount you gave and when it took place. A credit card statement, canceled check or a written receipt from the museum will all do the trick. If you donate $250 or more, you need a written acknowledgement from the museum describing your donation.