MFAAX vs. FNBGX

Last updated Jun 4, 2026

MFAAX (American Funds Mortgage Fund) and FNBGX (Fidelity Long-Term Treasury Bond Index Fund) are both Government Bonds funds. Over the past 5 years, MFAAX returned 0.09%/yr vs -5.10%/yr for FNBGX. A 0.77 correlation means they provide meaningful diversification when combined. MFAAX charges 0.64%/yr vs 0.03%/yr for FNBGX.

Performance

MFAAX vs. FNBGX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in American Funds Mortgage Fund (MFAAX) and Fidelity Long-Term Treasury Bond Index Fund (FNBGX). 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 FNBGX's 0.02% 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%

FNBGX

• 1D: 0.22%
• 1M: 1.23%
• YTD: 0.02%
• 6M: -1.23%
• 1Y: 5.75%
• 3Y*: -0.54%
• 5Y*: -5.10%
• 10Y*: —

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

MFAAX vs. FNBGX - 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%	-0.45%
FNBGX Fidelity Long-Term Treasury Bond Index Fund	0.02%	5.30%	-6.18%	3.20%	-29.89%	-5.17%	17.58%	14.24%	-1.62%	1.86%

Correlation

The correlation between MFAAX and FNBGX is 0.83, indicating a strong positive relationship between their price movements. Combining them offers limited diversification - they tend to fall together during downturns.

	Correlation
Correlation (1Y) Calculated over the trailing 1-year period	0.83
Correlation (3Y) Calculated over the trailing 3-year period	0.85
Correlation (5Y) Calculated over the trailing 5-year period	0.83
Correlation (All Time) Calculated using the full available price history since Oct 20, 2017	0.77

The correlation between MFAAX and FNBGX has been stable across timeframes, ranging from 0.77 to 0.85 - a consistent structural relationship.

Return for Risk

MFAAX vs. FNBGX — 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

FNBGX

FNBGX Risk / Return Rank: 7
FNBGX Sharpe Ratio Rank: 8
FNBGX Sortino Ratio Rank: 7
FNBGX Omega Ratio Rank: 7
FNBGX Calmar Ratio Rank: 8
FNBGX Martin Ratio Rank: 7

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. FNBGX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for American Funds Mortgage Fund (MFAAX) and Fidelity Long-Term Treasury Bond Index Fund (FNBGX). 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	FNBGX	Difference
Sharpe ratio: Return per unit of total volatility	1.27	0.63	+0.64
Sortino ratio: Return per unit of downside risk	1.95	0.96	+1.00
Omega ratio: Gain probability vs. loss probability	1.23	1.11	+0.12
Calmar ratio: Return relative to maximum drawdown	1.60	0.78	+0.82
Martin ratio: Return relative to average drawdown	5.22	2.06	+3.17
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. FNBGX - Sharpe Ratio Comparison

The current MFAAX Sharpe Ratio is 1.27, which is higher than the FNBGX Sharpe Ratio of 0.63. The chart below compares the historical Sharpe Ratios of MFAAX and FNBGX, 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	FNBGX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	1.27	0.63	+0.64
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.01	-0.35	+0.36
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	0.25	—	—
Sharpe Ratio (All Time) Calculated using the full available price history	0.39	-0.07	+0.47

Drawdowns

MFAAX vs. FNBGX - Drawdown Comparison

The maximum MFAAX drawdown since its inception was -16.60%, smaller than the maximum FNBGX drawdown of -46.86%. Use the drawdown chart below to compare losses from any high point for MFAAX and FNBGX.

Drawdown Indicators

	MFAAX	FNBGX	Difference
Max Drawdown Largest peak-to-trough decline	-16.60%	-46.86%	+30.26%
Max Drawdown (1Y) Largest decline over 1 year	-3.33%	-7.28%	+3.95%
Max Drawdown (3Y) Largest decline over 3 years	-7.40%	-17.66%	+10.26%
Max Drawdown (5Y) Largest decline over 5 years	-16.60%	-41.54%	+24.94%
Max Drawdown (10Y) Largest decline over 10 years	-16.60%	—	—
Current Drawdown Current decline from peak	-1.78%	-37.24%	+35.46%
Average Drawdown Average peak-to-trough decline	-2.62%	-21.65%	+19.03%
Ulcer Index Depth and duration of drawdowns from previous peaks	1.02%	2.74%	-1.72%

Volatility

MFAAX vs. FNBGX - Volatility Comparison

The current volatility for American Funds Mortgage Fund (MFAAX) is 1.58%, while Fidelity Long-Term Treasury Bond Index Fund (FNBGX) has a volatility of 2.79%. This indicates that MFAAX experiences smaller price fluctuations and is considered to be less risky than FNBGX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	MFAAX	FNBGX	Difference
Volatility (1M) Calculated over the trailing 1-month period	1.58%	2.79%	-1.21%
Volatility (6M) Calculated over the trailing 6-month period	2.94%	6.13%	-3.19%
Volatility (1Y) Calculated over the trailing 1-year period	4.20%	9.03%	-4.83%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	6.39%	14.59%	-8.20%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	4.82%	14.20%	-9.38%

MFAAX vs. FNBGX - Expense Ratio Comparison

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

Dividends

MFAAX vs. FNBGX - Dividend Comparison

MFAAX's dividend yield for the trailing twelve months is around 4.18%, more than FNBGX's 4.00% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
FNBGX Fidelity Long-Term Treasury Bond Index Fund	4.00%	3.88%	3.75%	3.20%	2.26%	2.47%	3.96%	2.63%	2.93%	0.70%	0.00%	0.00%
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 FNBGX in my portfolio?

MFAAX and FNBGX have a correlation of 0.83, 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 FNBGX?

FNBGX has higher volatility (2.79%) compared to MFAAX (1.58%). In terms of maximum drawdown, MFAAX dropped -16.60% vs FNBGX's -46.86%.

Which has better risk-adjusted returns?

MFAAX currently has the higher Sharpe Ratio (1.27 vs 0.63), 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.