SUB vs. MFLX

Last updated Aug 2, 2026

SUB (iShares Short-Term National Muni Bond ETF) and MFLX (First Trust Flexible Municipal High Income ETF) are both Municipal Bonds funds. SUB is passively managed, while MFLX is actively managed. Over the past 5 years, SUB returned 1.40%/yr vs -0.88%/yr for MFLX. Their 0.28 correlation means their historical movements had little consistent relationship. SUB charges 0.07%/yr vs 0.88%/yr for MFLX.

Performance

SUB vs. MFLX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in iShares Short-Term National Muni Bond ETF (SUB) and First Trust Flexible Municipal High Income ETF (MFLX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, SUB achieves a 0.76% return, which is significantly lower than MFLX's 1.98% return.

SUB

• 1D: 0.01%
• 1M: -0.15%
• 6M: 0.19%
• YTD: 0.76%
• 1Y: 1.85%
• 3Y*: 3.00%
• 5Y*: 1.40%
• 10Y*: 1.42%
• ALL TIME*: 1.58%

MFLX

• 1D: -0.12%
• 1M: -2.47%
• 6M: 1.03%
• YTD: 1.98%
• 1Y: 7.47%
• 3Y*: 5.09%
• 5Y*: -0.88%
• 10Y*: —
• ALL TIME*: 1.97%

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

Liquidity Comparison

Position	Avg. Volume Value (2W)	Avg. Volume Value (1M)	Avg. Volume Value (3M)
MFLX First Trust Flexible Municipal High Income ETF	$144.82K	$125.46K	$116.25K
SUB iShares Short-Term National Muni Bond ETF	$44.46M	$43.86M	$47.41M

SUB vs. MFLX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
SUB iShares Short-Term National Muni Bond ETF	0.76%	3.64%	2.17%	2.91%	-2.05%	0.03%	2.51%	2.93%	1.85%	0.75%
MFLX First Trust Flexible Municipal High Income ETF	1.98%	3.94%	3.74%	8.98%	-19.94%	8.43%	7.19%	16.89%	-4.66%	5.57%

Correlation

The correlation between SUB and MFLX is 0.41, which is low. Their historical price movements had little consistent relationship.

	Correlation
Correlation (1Y) Focuses on recent behavior, but can change the most.	0.41
Correlation (3Y) Balances recent behavior with more history.	0.35
Correlation (5Y) Shows whether the relationship held over a longer period.	0.33
Correlation (All Time) Calculated using the full available price history since Sep 29, 2016	0.28

The correlation between SUB and MFLX shifts across timeframes, from 0.28 (all time) to 0.41 (1 year), reflecting how their relationship changes across market environments.

Return for Risk

SUB vs. MFLX — Risk / Return Rank

Compare historical risk-adjusted metric ranks over the past 12 months.

SUB

SUB Risk / Return Rank: 74
SUB Sharpe Ratio Rank: 79
SUB Sortino Ratio Rank: 78
SUB Omega Ratio Rank: 85
SUB Calmar Ratio Rank: 72
SUB Martin Ratio Rank: 58

MFLX

MFLX Risk / Return Rank: 81
MFLX Sharpe Ratio Rank: 82
MFLX Sortino Ratio Rank: 85
MFLX Omega Ratio Rank: 89
MFLX Calmar Ratio Rank: 71
MFLX Martin Ratio Rank: 76

The rank (0–100) uses a weighted average of the Sharpe, Sortino, Omega, Calmar, and Martin percentile ranks for the trailing 12 months. Higher means stronger historical risk-adjusted performance within the peer group.

SUB vs. MFLX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for iShares Short-Term National Muni Bond ETF (SUB) and First Trust Flexible Municipal High Income ETF (MFLX). 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.

	SUB	MFLX	Difference
Sharpe ratio: Return per unit of total volatility	1.80	1.90	-0.11
Sortino ratio: Return per unit of downside risk	2.50	2.82	-0.32
Omega ratio: Gain probability vs. loss probability	1.37	1.41	-0.04
Calmar ratio: Return relative to maximum drawdown	2.50	2.49	+0.01
Martin ratio: Return relative to average drawdown	6.88	9.54	-2.66

SUB vs. MFLX - Sharpe Ratio Comparison

The current SUB Sharpe Ratio is 1.80, which is comparable to the MFLX Sharpe Ratio of 1.90. The chart below compares the historical Sharpe Ratios of SUB and MFLX, 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

SUB vs. MFLX - Drawdown Comparison

The maximum SUB drawdown since its inception was -9.46%, smaller than the maximum MFLX drawdown of -26.76%. Use the drawdown chart below to compare losses from any high point for SUB and MFLX.

Drawdown Indicators

	SUB	MFLX	Difference
Max Drawdown Largest peak-to-trough decline	-9.46%	-26.76%	+17.30%
Max Drawdown (1Y) Largest decline over 1 year	-0.81%	-3.11%	+2.30%
Max Drawdown (3Y) Largest decline over 3 years	-1.23%	-7.36%	+6.13%
Max Drawdown (5Y) Largest decline over 5 years	-4.33%	-25.88%	+21.55%
Max Drawdown (10Y) Largest decline over 10 years	-9.46%	—	—
Current Drawdown Current decline from peak	-0.20%	-5.04%	+4.84%
Average Drawdown Average peak-to-trough decline	-0.91%	-8.09%	+7.18%
Ulcer Index Depth and duration of drawdowns from previous peaks	0.29%	0.81%	-0.52%

Volatility

SUB vs. MFLX - Volatility Comparison

The current volatility for iShares Short-Term National Muni Bond ETF (SUB) is 0.51%, while First Trust Flexible Municipal High Income ETF (MFLX) has a volatility of 1.08%. This indicates that SUB experiences smaller price fluctuations and is considered to be less risky than MFLX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	SUB	MFLX	Difference
Volatility (1M) Calculated over the trailing 1-month period	0.51%	1.08%	-0.57%
Volatility (6M) Calculated over the trailing 6-month period	0.90%	3.24%	-2.34%
Volatility (1Y) Calculated over the trailing 1-year period	1.12%	4.11%	-2.99%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	1.65%	10.33%	-8.68%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	2.60%	11.21%	-8.61%

SUB vs. MFLX - Expense Ratio Comparison

SUB has a 0.07% expense ratio, which is lower than MFLX's 0.88% expense ratio.

Dividends

SUB vs. MFLX - Dividend Comparison

SUB's dividend yield for the trailing twelve months is around 2.54%, less than MFLX's 4.20% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
MFLX First Trust Flexible Municipal High Income ETF	4.20%	4.06%	3.81%	3.65%	4.27%	3.69%	3.21%	2.94%	3.74%	3.80%	0.98%	0.00%
SUB iShares Short-Term National Muni Bond ETF	2.34%	2.42%	2.10%	1.73%	0.86%	0.72%	1.23%	1.58%	1.32%	0.95%	0.75%	0.77%

Frequently Asked Questions

Can I hold both SUB and MFLX in my portfolio?

SUB and MFLX have a correlation of 0.41, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, SUB or MFLX?

MFLX has higher volatility (1.08%) compared to SUB (0.51%). In terms of maximum drawdown, SUB dropped -9.46% vs MFLX's -26.76%.

Which ETF is better, SUB or MFLX?

On 5-year performance, SUB leads with 1.40% vs -0.88% for MFLX. On fees, SUB is cheaper at 0.07% per year. On volatility, SUB has been the lower-risk option at 0.51%. The better choice depends on whether you care most about return, fees, risk, or income.

Which ETF has performed better, SUB or MFLX?

Over the 5-year period, SUB has performed better with a 1.40% return vs -0.88%. Past performance does not guarantee future results, so compare this with risk, fees, and fund exposure.

Which ETF is cheaper, SUB or MFLX?

SUB is cheaper with a 0.07% expense ratio, compared with 0.88% for MFLX.

Which ETF pays a higher dividend yield, SUB or MFLX?

MFLX has the higher dividend yield at 4.20%, compared with 2.34% for SUB.

What is the main difference between SUB and MFLX?

They also come from different issuers: iShares and First Trust. Their fees differ too: 0.07% for SUB and 0.88% for MFLX.

Which has better risk-adjusted returns?

MFLX currently has the higher Sharpe Ratio (1.90 vs 1.80), 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.