MFAAX vs. FBLTX

Last updated Jun 4, 2026

MFAAX (American Funds Mortgage Fund) and FBLTX (Fidelity SAI Long-Term Treasury Bond Index Fund) are both Government Bonds funds. Over the past 10 years, MFAAX returned 1.20%/yr vs -1.68%/yr for FBLTX. A 0.74 correlation means they provide meaningful diversification when combined. MFAAX charges 0.64%/yr vs 0.03%/yr for FBLTX.

Performance

MFAAX vs. FBLTX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in American Funds Mortgage Fund (MFAAX) and Fidelity SAI Long-Term Treasury Bond Index Fund (FBLTX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, MFAAX achieves a -0.24% return, which is significantly lower than FBLTX's -0.08% return. Over the past 10 years, MFAAX has outperformed FBLTX with an annualized return of 1.20%, while FBLTX has yielded a comparatively lower -1.68% annualized return.

MFAAX

• 1D: 0.00%
• 1M: 0.22%
• YTD: -0.24%
• 6M: -0.01%
• 1Y: 5.31%
• 3Y*: 3.46%
• 5Y*: 0.09%
• 10Y*: 1.20%

FBLTX

• 1D: 0.15%
• 1M: 1.13%
• YTD: -0.08%
• 6M: -1.63%
• 1Y: 5.28%
• 3Y*: -1.70%
• 5Y*: -6.17%
• 10Y*: -1.68%

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

MFAAX vs. FBLTX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
MFAAX American Funds Mortgage Fund	-0.24%	8.46%	0.55%	2.87%	-10.52%	-0.64%	6.59%	4.70%	0.49%	1.35%
FBLTX Fidelity SAI Long-Term Treasury Bond Index Fund	-0.08%	4.39%	-8.05%	2.71%	-31.84%	-4.89%	18.27%	14.36%	-1.24%	9.06%

Correlation

The correlation between MFAAX and FBLTX is 0.80, which is moderate. They share some common price drivers but move independently often enough to provide real diversification benefit when combined.

	Correlation
Correlation (1Y) Calculated over the trailing 1-year period	0.80
Correlation (3Y) Calculated over the trailing 3-year period	0.83
Correlation (5Y) Calculated over the trailing 5-year period	0.81
Correlation (10Y) Calculated over the trailing 10-year period	0.75
Correlation (All Time) Calculated using the full available price history since Oct 19, 2015	0.74

The correlation between MFAAX and FBLTX has been stable across timeframes, ranging from 0.74 to 0.83 - a consistent structural relationship.

Return for Risk

MFAAX vs. FBLTX — Risk / Return Rank

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

MFAAX

MFAAX Risk / Return Rank: 20
MFAAX Sharpe Ratio Rank: 20
MFAAX Sortino Ratio Rank: 21
MFAAX Omega Ratio Rank: 20
MFAAX Calmar Ratio Rank: 19
MFAAX Martin Ratio Rank: 20

FBLTX

FBLTX Risk / Return Rank: 6
FBLTX Sharpe Ratio Rank: 7
FBLTX Sortino Ratio Rank: 6
FBLTX Omega Ratio Rank: 6
FBLTX Calmar Ratio Rank: 7
FBLTX Martin Ratio Rank: 6

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.

MFAAX vs. FBLTX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for American Funds Mortgage Fund (MFAAX) and Fidelity SAI Long-Term Treasury Bond Index Fund (FBLTX). 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.

	MFAAX	FBLTX	Difference
Sharpe ratio: Return per unit of total volatility	1.27	0.53	+0.75
Sortino ratio: Return per unit of downside risk	1.95	0.82	+1.13
Omega ratio: Gain probability vs. loss probability	1.23	1.09	+0.14
Calmar ratio: Return relative to maximum drawdown	1.60	0.67	+0.93
Martin ratio: Return relative to average drawdown	5.22	1.71	+3.52
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

MFAAX vs. FBLTX - Sharpe Ratio Comparison

The current MFAAX Sharpe Ratio is 1.27, which is higher than the FBLTX Sharpe Ratio of 0.53. The chart below compares the historical Sharpe Ratios of MFAAX and FBLTX, calculated using daily returns over the previous 12 months. A higher Sharpe Ratio indicates better risk-adjusted performance relative to the risk-free rate.

Sharpe Ratios by Period

	MFAAX	FBLTX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	1.27	0.53	+0.75
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.01	-0.39	+0.41
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	0.25	-0.12	+0.37
Sharpe Ratio (All Time) Calculated using the full available price history	0.39	-0.05	+0.45

Drawdowns

MFAAX vs. FBLTX - Drawdown Comparison

The maximum MFAAX drawdown since its inception was -16.60%, smaller than the maximum FBLTX drawdown of -49.06%. Use the drawdown chart below to compare losses from any high point for MFAAX and FBLTX.

Drawdown Indicators

	MFAAX	FBLTX	Difference
Max Drawdown Largest peak-to-trough decline	-16.60%	-49.06%	+32.46%
Max Drawdown (1Y) Largest decline over 1 year	-3.33%	-7.66%	+4.33%
Max Drawdown (3Y) Largest decline over 3 years	-7.40%	-19.12%	+11.72%
Max Drawdown (5Y) Largest decline over 5 years	-16.60%	-44.19%	+27.59%
Max Drawdown (10Y) Largest decline over 10 years	-16.60%	-49.06%	+32.46%
Current Drawdown Current decline from peak	-1.78%	-41.01%	+39.23%
Average Drawdown Average peak-to-trough decline	-2.62%	-20.99%	+18.37%
Ulcer Index Depth and duration of drawdowns from previous peaks	1.02%	3.01%	-1.99%

Volatility

MFAAX vs. FBLTX - Volatility Comparison

The current volatility for American Funds Mortgage Fund (MFAAX) is 1.58%, while Fidelity SAI Long-Term Treasury Bond Index Fund (FBLTX) has a volatility of 2.80%. This indicates that MFAAX experiences smaller price fluctuations and is considered to be less risky than FBLTX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	MFAAX	FBLTX	Difference
Volatility (1M) Calculated over the trailing 1-month period	1.58%	2.80%	-1.22%
Volatility (6M) Calculated over the trailing 6-month period	2.94%	6.56%	-3.62%
Volatility (1Y) Calculated over the trailing 1-year period	4.20%	9.82%	-5.62%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	6.39%	15.70%	-9.31%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	4.82%	14.59%	-9.77%

MFAAX vs. FBLTX - Expense Ratio Comparison

MFAAX has a 0.64% expense ratio, which is higher than FBLTX's 0.03% expense ratio.

Dividends

MFAAX vs. FBLTX - Dividend Comparison

MFAAX's dividend yield for the trailing twelve months is around 4.18%, which matches FBLTX's 4.17% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
FBLTX Fidelity SAI Long-Term Treasury Bond Index Fund	4.17%	4.04%	3.60%	3.29%	2.25%	1.81%	6.73%	2.39%	2.87%	2.68%	3.70%	0.39%
MFAAX American Funds Mortgage Fund	4.18%	4.18%	4.49%	3.24%	1.36%	0.33%	4.38%	2.90%	1.77%	1.65%	2.34%	2.44%

Frequently Asked Questions

Can I hold both MFAAX and FBLTX in my portfolio?

MFAAX and FBLTX have a correlation of 0.80, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, MFAAX or FBLTX?

FBLTX has higher volatility (2.80%) compared to MFAAX (1.58%). In terms of maximum drawdown, MFAAX dropped -16.60% vs FBLTX's -49.06%.

Which has better risk-adjusted returns?

MFAAX currently has the higher Sharpe Ratio (1.27 vs 0.53), meaning it's delivered slightly more return per unit of risk over the trailing 12 months. However, this ranking shifts over time - use the Risk/Return Score above for a more comprehensive view that combines Sharpe, Sortino, and other measures used by quantitative funds.