Money market funds.
After-tax yield comparison.
Compare SPAXX, FZFXX, FDLXX, HYSAs, T-bills, and CDs on an after-tax basis given your federal and state tax brackets. The right choice depends on your state.
The question it answersWhich cash option keeps more after taxes: SPAXX, FDLXX or a high-yield savings account?
Rules: United States. Privacy: runs in your browser. What you enter stays on your device unless you copy a share link, which puts your inputs in the link.
US-only. Yields and state-tax exemption rules are US-specific.
At a 9.3% California state rate, a $50,000 balance for 12 months. SPAXX at 3.30% gross with 0% state-exempt (it misses California's 50% U.S.-government-securities test): after-tax yield approximately 2.99%, interest earned approximately $1,497. FDLXX at 3.20% gross with 100% state-exempt: after-tax yield approximately 3.20%, interest earned approximately $1,600. FDLXX wins by about $103 on this balance. The advantage grows with higher state rates and larger balances.
| OPTION | GROSS | AFTER-TAX | INTEREST EARNED |
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Projection, not a promise. The result follows the assumptions you enter. Real results will differ, sometimes by a lot.
What this tool assumes
- after-tax yield = gross × (1 - federalRate - stateRate × (1 - stateExemptPct/100)).
- State-tax exemption applies only to the portion of yield from US Treasury obligations. SPAXX and FZFXX are partially exempt because they hold repurchase agreements alongside Treasuries; FDLXX is fully exempt because it holds Treasuries only; HYSAs and CDs are bank products with no state-tax exemption.
- Interest is treated as ordinary income at your federal marginal rate. State tax applies only to the non-exempt portion.
- FDIC vs SIPCSecurities Investor Protection Corporation (SIPC)When a member brokerage firm fails and customer assets are missing, most customers are protected up to $500,000, including $250,000 for cash. It does not cover a drop in a fund's value or any other market loss, and money market mutual funds count as securities, not cash.: HYSAs are FDIC-insured up to $250,000 per depositor, per insured bank, for each account ownership category. Government money market funds (SPAXX, FZFXX) hold US-government instruments but are not FDIC-insured. The SIPC protection on the brokerage account applies only if the member brokerage firm fails with customer assets missing (up to $500,000, including $250,000 for cash); it does not cover a drop in a fund's value verify×DON'T TRUST, VERIFYClaim: FDIC deposit insurance covers $250,000 per depositor, per insured bank, for each account ownership category, and money market funds are not FDIC-insured. SIPC protection is limited to $500,000, including $250,000 for cash, applies when a member brokerage firm fails with customer assets missing, and does not cover a decline in value.Verify at: FDIC: What We Do (Deposit Insurance) ↗ · SIPC: What SIPC Protects ↗ · SEC Investor.gov: Money Market Funds bulletin ↗ Source 2 in the list belowDeposit insurance and SIPC protect against different failures. FDIC covers deposits at a failed insured bank; SIPC restores missing securities and cash at a failed member brokerage firm. Neither covers a fund losing value..
HOW THIS IS CALCULATED
This tool runs entirely in your browser: no data is sent to any server. The assumptions and default values behind the result are listed under “What this tool assumes” on this page. Verify the methodology or inspect the source code in your browser's dev tools.
Where to go from here
Sources
Verify badges in the text link to these sources. Figures, rates and rules change: check each source’s date before acting on it.
- Fidelity Investments, SPAXX ↩
- Federal Deposit Insurance Corporation, FDIC: What We Do (Deposit Insurance) ↩
Calculators are educational estimates, not financial advice. Disclosures · How pages are reviewed