MFSM vs. MUB

Last updated Jun 3, 2026

MFSM (MFS Active Intermediate Muni Bond ETF) and MUB (iShares National AMT-Free Muni Bond ETF) are both Municipal Bonds funds. MFSM is actively managed, while MUB is passively managed. Over the past year, MFSM returned 7.56% vs 7.06% for MUB. Their correlation of 0.84 suggests significant overlap in exposure. MFSM charges 0.34%/yr vs 0.07%/yr for MUB.

Performance

MFSM vs. MUB - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in MFS Active Intermediate Muni Bond ETF (MFSM) and iShares National AMT-Free Muni Bond ETF (MUB). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, MFSM achieves a 1.76% return, which is significantly higher than MUB's 1.32% return.

MFSM

• 1D: 0.11%
• 1M: 0.64%
• YTD: 1.76%
• 6M: 2.32%
• 1Y: 7.56%
• 3Y*: —
• 5Y*: —
• 10Y*: —

MUB

• 1D: 0.15%
• 1M: 0.53%
• YTD: 1.32%
• 6M: 1.88%
• 1Y: 7.06%
• 3Y*: 3.46%
• 5Y*: 0.91%
• 10Y*: 2.00%

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

MFSM vs. MUB - Yearly Performance Comparison

	2026 (YTD)	2025	2024
MFSM MFS Active Intermediate Muni Bond ETF	1.76%	5.25%	-1.30%
MUB iShares National AMT-Free Muni Bond ETF	1.32%	3.78%	-1.47%

Correlation

The correlation between MFSM and MUB is 0.85, 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	0.85
Correlation (All Time) Calculated using the full available price history since Dec 6, 2024	0.84

The correlation between MFSM and MUB has been stable across timeframes, ranging from 0.84 to 0.85 - a consistent structural relationship.

Return for Risk

MFSM vs. MUB — Risk / Return Rank

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

MFSM

MFSM Risk / Return Rank: 76
MFSM Sharpe Ratio Rank: 85
MFSM Sortino Ratio Rank: 90
MFSM Omega Ratio Rank: 91
MFSM Calmar Ratio Rank: 55
MFSM Martin Ratio Rank: 58

MUB

MUB Risk / Return Rank: 67
MUB Sharpe Ratio Rank: 74
MUB Sortino Ratio Rank: 78
MUB Omega Ratio Rank: 84
MUB Calmar Ratio Rank: 48
MUB Martin Ratio Rank: 50

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.

MFSM vs. MUB - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for MFS Active Intermediate Muni Bond ETF (MFSM) and iShares National AMT-Free Muni Bond ETF (MUB). 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.

	MFSM	MUB	Difference
Sharpe ratio Return per unit of total volatility	2.84	2.43	+0.41
Sortino ratio Return per unit of downside risk	4.35	3.55	+0.80
Omega ratio Gain probability vs. loss probability	1.62	1.51	+0.11
Calmar ratio Return relative to maximum drawdown	2.80	2.42	+0.38
Martin ratio Return relative to average drawdown	10.40	8.59	+1.81
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

MFSM vs. MUB - Sharpe Ratio Comparison

The current MFSM Sharpe Ratio is 2.84, which is comparable to the MUB Sharpe Ratio of 2.43. The chart below compares the historical Sharpe Ratios of MFSM and MUB, 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

	MFSM	MUB	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	2.84	2.43	+0.41
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	—	0.23	—
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	—	0.41	—
Sharpe Ratio (All Time) Calculated using the full available price history	1.12	0.58	+0.53

Drawdowns

MFSM vs. MUB - Drawdown Comparison

The maximum MFSM drawdown since its inception was -3.86%, smaller than the maximum MUB drawdown of -13.68%. Use the drawdown chart below to compare losses from any high point for MFSM and MUB.

Drawdown Indicators

	MFSM	MUB	Difference
Max Drawdown Largest peak-to-trough decline	-3.86%	-13.68%	+9.82%
Max Drawdown (1Y) Largest decline over 1 year	-2.65%	-2.79%	+0.14%
Max Drawdown (3Y) Largest decline over 3 years	—	-5.34%	—
Max Drawdown (5Y) Largest decline over 5 years	—	-11.88%	—
Max Drawdown (10Y) Largest decline over 10 years	—	-13.68%	—
Current Drawdown Current decline from peak	-0.49%	-0.62%	+0.13%
Average Drawdown Average peak-to-trough decline	-0.88%	-2.23%	+1.35%
Ulcer Index Depth and duration of drawdowns from previous peaks	0.71%	0.79%	-0.08%

Volatility

MFSM vs. MUB - Volatility Comparison

The current volatility for MFS Active Intermediate Muni Bond ETF (MFSM) is 0.93%, while iShares National AMT-Free Muni Bond ETF (MUB) has a volatility of 0.98%. This indicates that MFSM experiences smaller price fluctuations and is considered to be less risky than MUB based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	MFSM	MUB	Difference
Volatility (1M) Calculated over the trailing 1-month period	0.93%	0.98%	-0.05%
Volatility (6M) Calculated over the trailing 6-month period	1.97%	2.23%	-0.26%
Volatility (1Y) Calculated over the trailing 1-year period	2.67%	2.93%	-0.26%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	3.45%	4.06%	-0.61%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	3.45%	4.92%	-1.47%

MFSM vs. MUB - Expense Ratio Comparison

MFSM has a 0.34% expense ratio, which is higher than MUB's 0.07% expense ratio.

Dividends

MFSM vs. MUB - Dividend Comparison

MFSM's dividend yield for the trailing twelve months is around 3.55%, more than MUB's 3.17% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
MFSM MFS Active Intermediate Muni Bond ETF	3.55%	3.53%	0.23%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
MUB iShares National AMT-Free Muni Bond ETF	3.17%	3.14%	3.01%	2.65%	2.11%	1.81%	2.11%	2.42%	2.46%	2.26%	2.21%	2.51%

Frequently Asked Questions

Can I hold both MFSM and MUB in my portfolio?

MFSM and MUB have a correlation of 0.85, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, MFSM or MUB?

MUB has higher volatility (0.98%) compared to MFSM (0.93%). In terms of maximum drawdown, MFSM dropped -3.86% vs MUB's -13.68%.

Which ETF is better, MFSM or MUB?

On 1-year performance, MFSM leads with 7.56% vs 7.06% for MUB. On fees, MUB is cheaper at 0.07% per year. Their volatility is very similar. The better choice depends on whether you care most about return, fees, risk, or income.

Which ETF has performed better, MFSM or MUB?

Over the 1-year period, MFSM has performed better with a 7.56% return vs 7.06%. Past performance does not guarantee future results, so compare this with risk, fees, and fund exposure.

Which ETF is cheaper, MFSM or MUB?

MUB is cheaper with a 0.07% expense ratio, compared with 0.34% for MFSM.

Which ETF pays a higher dividend yield, MFSM or MUB?

MFSM has the higher dividend yield at 3.55%, compared with 3.17% for MUB.

What is the main difference between MFSM and MUB?

They also come from different issuers: MFS and iShares. Their fees differ too: 0.34% for MFSM and 0.07% for MUB.

Which has better risk-adjusted returns?

MFSM currently has the higher Sharpe Ratio (2.84 vs 2.43), 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.