If you live in California and hold the iShares California Muni Bond ETF (ticker CMF), the monthly interest the fund pays you is exempt from both federal income tax and California state income tax. That double exemption is the headline tax benefit of CMF for a California resident, and in the top brackets it can make a 3% headline yield worth more than a 5%+ yield on a taxable bond. The exemption has edges, though. Capital gains when you sell, interest on money you borrow to buy shares, and the way tax-exempt interest flows into the Social Security benefit formula can all still create a bill.
The Federal Exemption on CMF’s Interest
Federal law excludes interest on state and local bonds from gross income.1Office of the Law Revision Counsel. 26 U.S. Code 103 – Interest on State and Local Bonds CMF holds a basket of investment-grade California municipal bonds, so the monthly distributions pass that exclusion through to shareholders. You owe no federal income tax on that interest, no matter which state you live in.
Tax-exempt is not the same as invisible. Your brokerage reports CMF’s exempt interest in box 8 of Form 1099-INT, and you enter the total on Line 2a of Form 1040.2Internal Revenue Service. Instructions for Schedule B (Form 1040) (2025) The IRS wants the number on the return even though it is not added to taxable income, because it feeds other calculations further down the form.
The California Exemption for In-State Residents
California does not tax its residents on interest from bonds issued by California and its local governments. Because that is exactly what CMF holds, the fund’s distributions escape California’s personal income tax as well as the federal tax. California’s top marginal rate reaches 13.3% on income above $1 million, built from a 12.3% top bracket plus the 1% Mental Health Services Act surcharge, so skipping state tax on a steady income stream matters at the top of the schedule.3California Franchise Tax Board. 2025 California Tax Rate Schedules
This is why the California-specific fund exists. A national muni ETF or a New York fund would deliver federally exempt interest, but California would tax most of it at your regular state rate. If you move out of California, you keep the federal exemption on CMF but lose the state side, and your new state may tax the interest the way California taxes out-of-state muni income. The fund is purpose-built for California residents.
What the Benefit Is Actually Worth: Tax-Equivalent Yield
To see whether CMF beats a taxable bond fund for you, convert its yield to a tax-equivalent yield: divide CMF’s yield by one minus your combined marginal rate.
Take a California resident in the 35% federal bracket and the 9.3% state bracket. The combined marginal rate on taxable interest lands near 44.3% once you account for the partial federal offset of state taxes. If CMF yields 3.2%, the tax-equivalent yield is 3.2% ÷ (1 − 0.443), or about 5.74%. A taxable bond fund would need to pay nearly 5.75% to match CMF after taxes. Run the same calculation at your own brackets. The higher you sit, the wider CMF’s advantage.
CMF Is AMT-Free by Design
CMF’s full name is the iShares California AMT-Free Muni Bond ETF. The fund screens out private activity bonds, whose interest counts as a tax preference item under the Alternative Minimum Tax and must be added back when computing AMT liability.4Office of the Law Revision Counsel. 26 U.S.C. 57 – Items of Tax Preference Because CMF excludes those bonds, its distributions should not create AMT exposure. If you also hold a muni fund that does include private activity bonds, that other fund’s income could still pull you into AMT, so the AMT-free label applies to CMF specifically, not to your muni holdings as a whole.
Where the Exemption Stops
The tax-exempt treatment covers CMF’s interest distributions. Several other tax items are untouched by it.
Capital Gains When You Sell Shares
Share price changes are not interest. If you buy CMF at $55 and sell at $60, the $5 per share is a capital gain subject to both federal and California tax. Federal long-term rates (shares held more than a year) are 0%, 15%, or 20%, depending on your taxable income.5Office of the Law Revision Counsel. 26 U.S.C. 1 – Tax Imposed Short-term gains are taxed at ordinary rates. California taxes capital gains as ordinary income regardless of holding period, so there is no preferential state rate. Keep clean records of purchase price and dates.
Interest on Money Borrowed to Buy CMF
If you buy CMF on margin or with a home equity line, you cannot deduct the interest on that borrowing. Federal law bars deducting interest on debt incurred to purchase or carry obligations whose income is tax-exempt.6Office of the Law Revision Counsel. 26 U.S.C. 265 – Expenses and Interest Relating to Tax-Exempt Income Factor the lost deduction into any decision to use borrowed money for the position.
Wash Sales If You Harvest Losses
If you sell CMF at a loss and buy it back (or buy a substantially identical fund) within 30 days before or after the sale, the IRS disallows the loss and adds it to the cost basis of the replacement shares.7Office of the Law Revision Counsel. 26 U.S.C. 1091 – Loss From Wash Sales of Stock or Securities Whether a different California muni ETF counts as substantially identical to CMF is not spelled out in the statute, and the IRS has not issued definitive guidance on ETF-to-ETF swaps. If you want to tax-loss harvest by rotating into a competing California muni fund, consider getting a tax professional involved.
The Social Security Benefit Formula
This one catches retirees off guard. Tax-exempt interest is explicitly included in the combined-income formula used to decide whether Social Security benefits become taxable. The formula adds one-half of your Social Security benefits to all other income, and tax-exempt interest is on the list. If the total exceeds $25,000 for single filers or $32,000 for married couples filing jointly, a portion of your benefits gets pulled into taxable income.8Internal Revenue Service. Social Security Income CMF’s interest stays tax-free, but it can still push the Social Security side of your return into taxable territory. If you are near those thresholds, model the effect before loading up on the fund.
Net Investment Income Tax
The 3.8% Net Investment Income Tax applies to the lesser of your net investment income or the amount by which modified adjusted gross income exceeds $200,000 single or $250,000 married filing jointly.9Office of the Law Revision Counsel. 26 U.S.C. 1411 – Imposition of Tax Tax-exempt muni interest is excluded from net investment income for this calculation.10Internal Revenue Service. Topic No. 559, Net Investment Income Tax CMF’s distributions don’t trigger or increase the surtax, a quiet advantage over taxable bond funds whose interest both counts as investment income and inflates MAGI. Capital gains from selling CMF shares, though, do count for NIIT purposes, so a profitable sale above the MAGI threshold can draw the 3.8% on top of the regular capital gains rate.
A Benefit That Carries Into an Estate
If you hold CMF shares until death, your heirs receive a stepped-up basis equal to the fair market value on the date of death.11Office of the Law Revision Counsel. 26 U.S.C. 1014 – Basis of Property Acquired From a Decedent Unrealized gains built up during your lifetime are wiped out for income tax purposes, and the heirs owe capital gains tax only on appreciation after they inherit. For a long-held CMF position with substantial embedded gains, that step-up sits on top of years of exempt interest and makes the fund an efficient vehicle for a California resident thinking past their own tax return.