AFTEX vs. MMIBX

Last updated Jun 23, 2026

AFTEX (American Funds Tax Exempt Bond Fund) and MMIBX (MFS Municipal Income Fund) are both Municipal Bonds funds. Over the past 10 years, AFTEX returned 2.13%/yr vs 1.47%/yr for MMIBX. Their correlation of 0.80 suggests significant overlap in exposure. AFTEX charges 0.50%/yr vs 1.45%/yr for MMIBX.

Performance

AFTEX vs. MMIBX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in American Funds Tax Exempt Bond Fund (AFTEX) and MFS Municipal Income Fund (MMIBX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, AFTEX achieves a 1.66% return, which is significantly lower than MMIBX's 1.75% return. Over the past 10 years, AFTEX has outperformed MMIBX with an annualized return of 2.13%, while MMIBX has yielded a comparatively lower 1.47% annualized return.

AFTEX

• 1D: 0.08%
• 1M: 1.64%
• YTD: 1.66%
• 6M: 2.01%
• 1Y: 6.67%
• 3Y*: 4.13%
• 5Y*: 0.92%
• 10Y*: 2.13%

MMIBX

• 1D: 0.00%
• 1M: 1.87%
• YTD: 1.75%
• 6M: 2.13%
• 1Y: 6.67%
• 3Y*: 3.59%
• 5Y*: -0.00%
• 10Y*: 1.47%

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

AFTEX vs. MMIBX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
AFTEX American Funds Tax Exempt Bond Fund	1.66%	4.88%	2.28%	5.96%	-9.68%	1.87%	4.73%	7.42%	0.78%	5.83%
MMIBX MFS Municipal Income Fund	1.75%	3.56%	2.42%	5.45%	-12.27%	2.35%	3.28%	7.40%	0.38%	5.00%

Correlation

The correlation between AFTEX and MMIBX is 0.87, 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	0.87
Correlation (3Y) Calculated over the trailing 3-year period	0.91
Correlation (5Y) Calculated over the trailing 5-year period	0.92
Correlation (10Y) Calculated over the trailing 10-year period	0.89
Correlation (All Time) Calculated using the full available price history since Jan 2, 1990	0.80

The correlation between AFTEX and MMIBX shifts across timeframes, from 0.80 (all time) to 0.92 (5 years), reflecting how their relationship changes across market environments.

Return for Risk

AFTEX vs. MMIBX — Risk / Return Rank

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

AFTEX

AFTEX Risk / Return Rank: 70
AFTEX Sharpe Ratio Rank: 85
AFTEX Sortino Ratio Rank: 90
AFTEX Omega Ratio Rank: 91
AFTEX Calmar Ratio Rank: 44
AFTEX Martin Ratio Rank: 42

MMIBX

MMIBX Risk / Return Rank: 60
MMIBX Sharpe Ratio Rank: 63
MMIBX Sortino Ratio Rank: 77
MMIBX Omega Ratio Rank: 85
MMIBX Calmar Ratio Rank: 38
MMIBX Martin Ratio Rank: 36

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.

AFTEX vs. MMIBX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for American Funds Tax Exempt Bond Fund (AFTEX) and MFS Municipal Income Fund (MMIBX). 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.

Values are calculated on a 1-year rolling basis and updated daily. Risk-adjusted metrics are more stable over longer periods — use the period switch above to explore them.

	AFTEX	MMIBX	Difference
Sharpe ratio: Return per unit of total volatility	2.58	2.15	+0.43
Sortino ratio: Return per unit of downside risk	4.06	3.37	+0.69
Omega ratio: Gain probability vs. loss probability	1.64	1.53	+0.11
Calmar ratio: Return relative to maximum drawdown	2.43	2.23	+0.20
Martin ratio: Return relative to average drawdown	8.42	7.49	+0.93

AFTEX vs. MMIBX - Sharpe Ratio Comparison

The current AFTEX Sharpe Ratio is 2.58, which is comparable to the MMIBX Sharpe Ratio of 2.15. The chart below compares the historical Sharpe Ratios of AFTEX and MMIBX, calculated using daily returns over the previous 12 months. A higher Sharpe Ratio indicates better risk-adjusted performance relative to the risk-free rate.

Drawdowns

AFTEX vs. MMIBX - Drawdown Comparison

The maximum AFTEX drawdown since its inception was -14.55%, smaller than the maximum MMIBX drawdown of -17.40%. Use the drawdown chart below to compare losses from any high point for AFTEX and MMIBX.

Drawdown Indicators

	AFTEX	MMIBX	Difference
Max Drawdown Largest peak-to-trough decline	-14.55%	-17.40%	+2.85%
Max Drawdown (1Y) Largest decline over 1 year	-2.76%	-3.01%	+0.25%
Max Drawdown (3Y) Largest decline over 3 years	-5.21%	-7.23%	+2.02%
Max Drawdown (5Y) Largest decline over 5 years	-14.55%	-17.19%	+2.64%
Max Drawdown (10Y) Largest decline over 10 years	-14.55%	-17.19%	+2.64%
Current Drawdown Current decline from peak	-0.34%	-0.89%	+0.55%
Average Drawdown Average peak-to-trough decline	-1.66%	-2.81%	+1.15%
Ulcer Index Depth and duration of drawdowns from previous peaks	0.79%	0.89%	-0.10%

Volatility

AFTEX vs. MMIBX - Volatility Comparison

The current volatility for American Funds Tax Exempt Bond Fund (AFTEX) is 0.71%, while MFS Municipal Income Fund (MMIBX) has a volatility of 0.79%. This indicates that AFTEX experiences smaller price fluctuations and is considered to be less risky than MMIBX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	AFTEX	MMIBX	Difference
Volatility (1M) Calculated over the trailing 1-month period	0.71%	0.79%	-0.08%
Volatility (6M) Calculated over the trailing 6-month period	1.99%	2.33%	-0.34%
Volatility (1Y) Calculated over the trailing 1-year period	2.60%	3.12%	-0.52%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	3.76%	4.41%	-0.65%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	3.79%	4.34%	-0.55%

AFTEX vs. MMIBX - Expense Ratio Comparison

AFTEX has a 0.50% expense ratio, which is lower than MMIBX's 1.45% expense ratio.

Dividends

AFTEX vs. MMIBX - Dividend Comparison

AFTEX's dividend yield for the trailing twelve months is around 3.01%, more than MMIBX's 2.95% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
AFTEX American Funds Tax Exempt Bond Fund	3.01%	3.98%	2.90%	2.22%	1.75%	2.31%	2.43%	2.83%	2.86%	3.30%	2.90%	3.21%
MMIBX MFS Municipal Income Fund	2.95%	3.81%	2.51%	2.05%	1.42%	1.45%	1.86%	2.45%	2.68%	2.67%	2.87%	2.98%

Frequently Asked Questions

Can I hold both AFTEX and MMIBX in my portfolio?

AFTEX and MMIBX have a correlation of 0.87, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, AFTEX or MMIBX?

MMIBX has higher volatility (0.79%) compared to AFTEX (0.71%). In terms of maximum drawdown, AFTEX dropped -14.55% vs MMIBX's -17.40%.

Which has better risk-adjusted returns?

AFTEX currently has the higher Sharpe Ratio (2.58 vs 2.15), 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.