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.
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 60% state-exempt: after-tax yield approximately 3.12%, interest earned approximately $1,560. FZFXX at 3.20% gross with 100% state-exempt: after-tax yield approximately 3.20%, interest earned approximately $1,600. FZFXX wins by $40 on this balance. The advantage grows with higher state rates and larger balances.
| OPTION | GROSS | AFTER-TAX | INTEREST EARNED |
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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 is partially exempt because it holds repurchase agreements alongside Treasuries; FZFXX 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 SIPC: HYSAs are FDIC-insured up to $250,000. Government money market funds (SPAXX, FZFXX) are SIPC-protected as securities and hold US-government instruments, which are considered extremely safe but not FDIC-insured.
HOW THIS IS CALCULATED
This tool runs entirely in your browser — no data is sent to any server. All formulas use standard financial math. Verify the methodology or inspect the source code in your browser's dev tools.