Updated November 6, 2026 from live rates
FDLXX vs SPAXX: is Fidelity’s Treasury Only fund worth switching to?
At today's rates, FDLXX keeps more after tax in all 9 tax scenarios below, by about $157 to $980 a year on $500,000.
After-tax yield by tax situation
Yield you keep after federal and state income tax, at today's rates. The last column is the yearly gap between the best and second-best on $500,000. The 3.8% net investment income tax is left out; it lowers every taxable option by the same share.
| Federal bracket, state tax | FDLXX | SPAXX | Yearly gap |
|---|---|---|---|
| 24%, no state tax | 2.74% | 2.71% | $190 |
| 24%, 5% state | 2.74% | 2.62% | $615 |
| 24%, 9.3% state | 2.74% | 2.54% | $980 |
| 32%, no state tax | 2.45% | 2.42% | $170 |
| 32%, 5% state | 2.45% | 2.33% | $595 |
| 32%, 9.3% state | 2.45% | 2.26% | $960 |
| 37%, no state tax | 2.27% | 2.24% | $157 |
| 37%, 5% state | 2.27% | 2.16% | $582 |
| 37%, 9.3% state | 2.27% | 2.08% | $948 |
What's different
| FDLXX | SPAXX | |
|---|---|---|
| What it is | Treasury-only money fund (Fidelity)FDLXX, Fidelity Treasury Only Money Market Fund | Fidelity brokerage (SPAXX core)SPAXX, Fidelity Government Money Market |
| Rate today | 3.61%7-day yieldVerified October 30, 2026 | 3.56%7-day yieldVerified November 1, 2026 |
| Getting your money | Next business day | Same day |
| Protection | Money market fund, not FDIC-insured | Money market fund, not FDIC-insured |
| State income tax | 98.7% exempt (2025 notice) | 50.9% exempt (2025 notice) |
SPAXX is the default core position at Fidelity; FDLXX, the Treasury Only Money Market Fund, is one trade away in the same account. Fidelity's 2025 tax letter puts FDLXX's income at 98.67% from U.S. government securities and SPAXX's at 50.90%. In a state with income tax that difference usually outweighs the small gap in yield. FDLXX is bought, not used as the core position, so cash has to be moved into it.