PMMF vs. SPAXX

Last updated Apr 2, 2026

Compare and contrast key facts about iShares Prime Money Market ETF (PMMF) and Fidelity Government Money Market Fund (SPAXX).

PMMF is an actively managed fund by BlackRock. It was launched on Feb 4, 2025. SPAXX is managed by Fidelity. It was launched on Feb 5, 1990.

Performance

PMMF vs. SPAXX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in iShares Prime Money Market ETF (PMMF) and Fidelity Government Money Market Fund (SPAXX). The values are adjusted to include any dividend payments, if applicable.

PMMF vs. SPAXX - Yearly Performance Comparison

	2026 (YTD)	2025
PMMF iShares Prime Money Market ETF	0.88%	3.85%
SPAXX Fidelity Government Money Market Fund	0.53%	3.61%

Returns By Period

In the year-to-date period, PMMF achieves a 0.88% return, which is significantly higher than SPAXX's 0.53% return.

PMMF

• 1D: 0.02%
• 1M: 0.27%
• YTD: 0.88%
• 6M: 1.88%
• 1Y: 4.08%
• 3Y*: —
• 5Y*: —
• 10Y*: —

SPAXX

• 1D: 0.00%
• 1M: 0.00%
• YTD: 0.53%
• 6M: 1.46%
• 1Y: 3.49%
• 3Y*: 2.14%
• 5Y*: —
• 10Y*: —

*Multi-year figures are annualized to reflect compound growth (CAGR)

PMMF vs. SPAXX - Expense Ratio Comparison

PMMF

iShares Prime Money Market ETF

Return for Risk

PMMF vs. SPAXX — Risk / Return Rank

Compare risk-adjusted metric ranks to identify better-performing investments over the past 12 months.

PMMF

PMMF Risk / Return Rank: 100
PMMF Sharpe Ratio Rank: 100
PMMF Sortino Ratio Rank: 100
PMMF Omega Ratio Rank: 100
PMMF Calmar Ratio Rank: 99
PMMF Martin Ratio Rank: 100

The rank (0–100) shows how this investment's returns compare to the risk taken. Higher = better. Based on the past 12 months of data, combining Sharpe, Sortino, and other metrics used by quantitative funds and institutional investors.

PMMF vs. SPAXX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for iShares Prime Money Market ETF (PMMF) and Fidelity Government Money Market Fund (SPAXX). Risk-adjusted metrics are performance indicators that assess an investment's returns in relation to its risk, enabling a more accurate comparison of different investment options.

	PMMF	SPAXX	Difference
Sharpe ratio Return per unit of total volatility	13.41	3.48	+9.93
Sortino ratio Return per unit of downside risk	25.32	—	—
Omega ratio Gain probability vs. loss probability	11.73	—	—
Calmar ratio Return relative to maximum drawdown	31.58	—	—
Martin ratio Return relative to average drawdown	380.28	—	—
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

PMMF vs. SPAXX - Sharpe Ratio Comparison

The current PMMF Sharpe Ratio is 13.41, which is higher than the SPAXX Sharpe Ratio of 3.48. The chart below compares the historical Sharpe Ratios of PMMF and SPAXX, offering insights into how both investments have performed under varying market conditions. These values are calculated using daily returns over the previous 12 months.

Sharpe Ratios by Period

	PMMF	SPAXX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	13.41	3.48	+9.93
Sharpe Ratio (All Time) Calculated using the full available price history	11.54	2.01	+9.53

Correlation

The correlation between PMMF and SPAXX is -0.01. This indicates that the assets' prices tend to move in opposite directions. Negative correlation can be particularly beneficial for diversification and risk management, as one asset may offset the losses of the other during market fluctuations.

Dividends

PMMF vs. SPAXX - Dividend Comparison

PMMF's dividend yield for the trailing twelve months is around 3.88%, more than SPAXX's 3.42% yield.

	TTM	2025	2024	2023
PMMF iShares Prime Money Market ETF	3.88%	3.59%	0.00%	0.00%
SPAXX Fidelity Government Money Market Fund	3.42%	3.88%	1.53%	0.41%

Drawdowns

PMMF vs. SPAXX - Drawdown Comparison

The maximum PMMF drawdown since its inception was -0.13%, which is greater than SPAXX's maximum drawdown of 0.00%. Use the drawdown chart below to compare losses from any high point for PMMF and SPAXX.

Drawdown Indicators

	PMMF	SPAXX	Difference
Max Drawdown Largest peak-to-trough decline	-0.13%	0.00%	-0.13%
Max Drawdown (1Y) Largest decline over 1 year	-0.13%	0.00%	-0.13%
Current Drawdown Current decline from peak	0.00%	0.00%	0.00%
Average Drawdown Average peak-to-trough decline	0.00%	0.00%	0.00%
Ulcer Index Depth and duration of drawdowns from previous peaks	0.01%	0.00%	+0.01%

Volatility

PMMF vs. SPAXX - Volatility Comparison

iShares Prime Money Market ETF (PMMF) has a higher volatility of 0.05% compared to Fidelity Government Money Market Fund (SPAXX) at 0.00%. This indicates that PMMF's price experiences larger fluctuations and is considered to be riskier than SPAXX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	PMMF	SPAXX	Difference
Volatility (1M) Calculated over the trailing 1-month period	0.05%	0.00%	+0.05%
Volatility (6M) Calculated over the trailing 6-month period	0.13%	0.71%	-0.58%
Volatility (1Y) Calculated over the trailing 1-year period	0.31%	1.08%	-0.77%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	0.36%	0.67%	-0.31%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	0.36%	0.67%	-0.31%