MFLX vs. SUB

Last updated Apr 1, 2026

Compare and contrast key facts about First Trust Flexible Municipal High Income ETF (MFLX) and iShares Short-Term National Muni Bond ETF (SUB).

MFLX and SUB are both exchange-traded funds (ETFs), meaning they are traded on stock exchanges and can be bought and sold throughout the day. MFLX is an actively managed fund by First Trust. It was launched on Sep 27, 2016. SUB is a passively managed fund by iShares that tracks the performance of the ICE Short Maturity AMT-Free US National Municipal Index - Benchmark TR Gross. It was launched on Nov 5, 2008.

Performance

MFLX vs. SUB - Performance Comparison

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

MFLX vs. SUB - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
MFLX First Trust Flexible Municipal High Income ETF	-0.25%	3.94%	3.74%	8.98%	-19.94%	8.43%	7.19%	16.89%	-4.66%	5.57%
SUB iShares Short-Term National Muni Bond ETF	0.23%	3.64%	2.17%	2.91%	-2.05%	0.03%	2.51%	2.93%	1.85%	0.75%

Returns By Period

In the year-to-date period, MFLX achieves a -0.25% return, which is significantly lower than SUB's 0.23% return.

MFLX

• 1D: -0.00%
• 1M: -3.00%
• YTD: -0.25%
• 6M: 1.18%
• 1Y: 3.35%
• 3Y*: 4.46%
• 5Y*: 0.01%
• 10Y*: —

SUB

• 1D: 0.04%
• 1M: -0.66%
• YTD: 0.23%
• 6M: 1.01%
• 1Y: 3.37%
• 3Y*: 2.75%
• 5Y*: 1.39%
• 10Y*: 1.46%

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

MFLX vs. SUB - Expense Ratio Comparison

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

MFLX

First Trust Flexible Municipal High Income ETF

SUB

iShares Short-Term National Muni Bond ETF

Return for Risk

MFLX vs. SUB — Risk / Return Rank

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

MFLX

MFLX Risk / Return Rank: 24
MFLX Sharpe Ratio Rank: 23
MFLX Sortino Ratio Rank: 21
MFLX Omega Ratio Rank: 27
MFLX Calmar Ratio Rank: 25
MFLX Martin Ratio Rank: 23

SUB

SUB Risk / Return Rank: 92
SUB Sharpe Ratio Rank: 94
SUB Sortino Ratio Rank: 92
SUB Omega Ratio Rank: 97
SUB Calmar Ratio Rank: 89
SUB Martin Ratio Rank: 88

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.

MFLX vs. SUB - Risk-Adjusted Trends Comparison

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

	MFLX	SUB	Difference
Sharpe ratio Return per unit of total volatility	0.38	2.25	-1.86
Sortino ratio Return per unit of downside risk	0.58	2.71	-2.13
Omega ratio Gain probability vs. loss probability	1.11	1.61	-0.50
Calmar ratio Return relative to maximum drawdown	0.56	2.82	-2.26
Martin ratio Return relative to average drawdown	1.69	10.30	-8.61
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

MFLX vs. SUB - Sharpe Ratio Comparison

The current MFLX Sharpe Ratio is 0.38, which is lower than the SUB Sharpe Ratio of 2.25. The chart below compares the historical Sharpe Ratios of MFLX and SUB, offering insights into how both investments have performed under varying market conditions. These values are calculated using daily returns over the previous 12 months.

Sharpe Ratios by Period

	MFLX	SUB	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	0.38	2.25	-1.86
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.00	0.85	-0.85
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	—	0.56	—
Sharpe Ratio (All Time) Calculated using the full available price history	0.16	0.42	-0.26

Correlation

The correlation between MFLX and SUB is 0.27, which is considered to be low. This implies their price changes are not closely related. A low correlation is generally favorable for portfolio diversification, as it helps to reduce overall risk by spreading it across multiple assets with different performance patterns.

Dividends

MFLX vs. SUB - Dividend Comparison

MFLX's dividend yield for the trailing twelve months is around 4.16%, more than SUB's 2.47% yield.

	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
MFLX First Trust Flexible Municipal High Income ETF	4.16%	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	2.47%	2.42%	2.10%	1.73%	0.86%	0.72%	1.23%	1.58%	1.32%	0.95%	0.75%	0.77%

Drawdowns

MFLX vs. SUB - Drawdown Comparison

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

Drawdown Indicators

	MFLX	SUB	Difference
Max Drawdown Largest peak-to-trough decline	-26.76%	-9.46%	-17.30%
Max Drawdown (1Y) Largest decline over 1 year	-6.64%	-1.23%	-5.41%
Max Drawdown (5Y) Largest decline over 5 years	-25.88%	-4.35%	-21.53%
Max Drawdown (10Y) Largest decline over 10 years	—	-9.46%	—
Current Drawdown Current decline from peak	-7.12%	-0.66%	-6.46%
Average Drawdown Average peak-to-trough decline	-8.23%	-0.92%	-7.31%
Ulcer Index Depth and duration of drawdowns from previous peaks	2.20%	0.34%	+1.86%

Volatility

MFLX vs. SUB - Volatility Comparison

First Trust Flexible Municipal High Income ETF (MFLX) has a higher volatility of 1.77% compared to iShares Short-Term National Muni Bond ETF (SUB) at 0.53%. This indicates that MFLX's price experiences larger fluctuations and is considered to be riskier than SUB based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	MFLX	SUB	Difference
Volatility (1M) Calculated over the trailing 1-month period	1.77%	0.53%	+1.24%
Volatility (6M) Calculated over the trailing 6-month period	2.40%	0.80%	+1.60%
Volatility (1Y) Calculated over the trailing 1-year period	8.77%	1.51%	+7.26%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	10.36%	1.64%	+8.72%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	11.38%	2.59%	+8.79%