MFSB vs. IUSB

Last updated Jun 5, 2026

MFSB (MFS Active Core Plus Bond ETF) and IUSB (iShares Core Universal USD Bond ETF) are both Intermediate Core-Plus Bond funds. MFSB is actively managed, while IUSB is passively managed. Over the past year, MFSB returned 5.70% vs 5.05% for IUSB. Their correlation of 0.94 suggests significant overlap in exposure. MFSB charges 0.34%/yr vs 0.06%/yr for IUSB.

Performance

MFSB vs. IUSB - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in MFS Active Core Plus Bond ETF (MFSB) and iShares Core Universal USD Bond ETF (IUSB). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, MFSB achieves a 0.74% return, which is significantly higher than IUSB's 0.56% return.

MFSB

• 1D: 0.18%
• 1M: 0.40%
• YTD: 0.74%
• 6M: 0.95%
• 1Y: 5.70%
• 3Y*: —
• 5Y*: —
• 10Y*: —

IUSB

• 1D: 0.13%
• 1M: 0.26%
• YTD: 0.56%
• 6M: 0.63%
• 1Y: 5.05%
• 3Y*: 4.56%
• 5Y*: 0.47%
• 10Y*: 1.97%

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

MFSB vs. IUSB - Yearly Performance Comparison

	2026 (YTD)	2025	2024
MFSB MFS Active Core Plus Bond ETF	0.74%	7.40%	-1.50%
IUSB iShares Core Universal USD Bond ETF	0.56%	7.38%	-1.73%

Correlation

The correlation between MFSB and IUSB is 0.94, 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	0.94
Correlation (All Time) Calculated using the full available price history since Dec 6, 2024	0.94

The correlation between MFSB and IUSB has been stable across timeframes, ranging from 0.94 to 0.94 - a consistent structural relationship.

Return for Risk

MFSB vs. IUSB — Risk / Return Rank

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

MFSB

MFSB Risk / Return Rank: 45
MFSB Sharpe Ratio Rank: 47
MFSB Sortino Ratio Rank: 48
MFSB Omega Ratio Rank: 45
MFSB Calmar Ratio Rank: 44
MFSB Martin Ratio Rank: 42

IUSB

IUSB Risk / Return Rank: 41
IUSB Sharpe Ratio Rank: 41
IUSB Sortino Ratio Rank: 43
IUSB Omega Ratio Rank: 39
IUSB Calmar Ratio Rank: 41
IUSB Martin Ratio Rank: 39

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.

MFSB vs. IUSB - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for MFS Active Core Plus Bond ETF (MFSB) and iShares Core Universal USD Bond ETF (IUSB). 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.

	MFSB	IUSB	Difference
Sharpe ratio: Return per unit of total volatility	1.59	1.42	+0.17
Sortino ratio: Return per unit of downside risk	2.33	2.11	+0.23
Omega ratio: Gain probability vs. loss probability	1.28	1.25	+0.03
Calmar ratio: Return relative to maximum drawdown	2.12	2.01	+0.11
Martin ratio: Return relative to average drawdown	6.62	6.08	+0.54
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

MFSB vs. IUSB - Sharpe Ratio Comparison

The current MFSB Sharpe Ratio is 1.59, which is comparable to the IUSB Sharpe Ratio of 1.42. The chart below compares the historical Sharpe Ratios of MFSB and IUSB, 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

	MFSB	IUSB	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	1.59	1.42	+0.17
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	—	0.08	—
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	—	0.39	—
Sharpe Ratio (All Time) Calculated using the full available price history	1.04	0.46	+0.58

Drawdowns

MFSB vs. IUSB - Drawdown Comparison

The maximum MFSB drawdown since its inception was -3.19%, smaller than the maximum IUSB drawdown of -17.90%. Use the drawdown chart below to compare losses from any high point for MFSB and IUSB.

Drawdown Indicators

	MFSB	IUSB	Difference
Max Drawdown Largest peak-to-trough decline	-3.19%	-17.90%	+14.71%
Max Drawdown (1Y) Largest decline over 1 year	-2.71%	-2.53%	-0.18%
Max Drawdown (3Y) Largest decline over 3 years	—	-5.82%	—
Max Drawdown (5Y) Largest decline over 5 years	—	-17.87%	—
Max Drawdown (10Y) Largest decline over 10 years	—	-17.90%	—
Current Drawdown Current decline from peak	-1.08%	-1.20%	+0.12%
Average Drawdown Average peak-to-trough decline	-0.82%	-3.59%	+2.77%
Ulcer Index Depth and duration of drawdowns from previous peaks	0.86%	0.83%	+0.03%

Volatility

MFSB vs. IUSB - Volatility Comparison

MFS Active Core Plus Bond ETF (MFSB) has a higher volatility of 1.33% compared to iShares Core Universal USD Bond ETF (IUSB) at 1.24%. This indicates that MFSB's price experiences larger fluctuations and is considered to be riskier than IUSB based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	MFSB	IUSB	Difference
Volatility (1M) Calculated over the trailing 1-month period	1.33%	1.24%	+0.09%
Volatility (6M) Calculated over the trailing 6-month period	2.69%	2.62%	+0.07%
Volatility (1Y) Calculated over the trailing 1-year period	3.64%	3.62%	+0.02%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	4.23%	5.79%	-1.56%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	4.23%	5.04%	-0.81%

MFSB vs. IUSB - Expense Ratio Comparison

MFSB has a 0.34% expense ratio, which is higher than IUSB's 0.06% expense ratio.

Dividends

MFSB vs. IUSB - Dividend Comparison

MFSB's dividend yield for the trailing twelve months is around 4.58%, more than IUSB's 4.23% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
IUSB iShares Core Universal USD Bond ETF	4.23%	4.17%	4.04%	3.46%	2.53%	1.74%	2.68%	3.04%	2.98%	2.56%	2.60%	1.95%
MFSB MFS Active Core Plus Bond ETF	4.58%	4.58%	0.37%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%

Frequently Asked Questions

Can I hold both MFSB and IUSB in my portfolio?

With a correlation of 0.94, MFSB and IUSB move almost identically. Holding both adds very little diversification - you're essentially doubling your position in the same market segment. Choosing one is usually more capital-efficient.

Which is riskier, MFSB or IUSB?

MFSB has higher volatility (1.33%) compared to IUSB (1.24%). In terms of maximum drawdown, MFSB dropped -3.19% vs IUSB's -17.90%.

Which ETF is better, MFSB or IUSB?

On 1-year performance, MFSB leads with 5.70% vs 5.05% for IUSB. On fees, IUSB is cheaper at 0.06% 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, MFSB or IUSB?

Over the 1-year period, MFSB has performed better with a 5.70% return vs 5.05%. Past performance does not guarantee future results, so compare this with risk, fees, and fund exposure.

Which ETF is cheaper, MFSB or IUSB?

IUSB is cheaper with a 0.06% expense ratio, compared with 0.34% for MFSB.

Which ETF pays a higher dividend yield, MFSB or IUSB?

MFSB has the higher dividend yield at 4.58%, compared with 4.23% for IUSB.

What is the main difference between MFSB and IUSB?

They also come from different issuers: MFS and iShares. Their fees differ too: 0.34% for MFSB and 0.06% for IUSB.

Which has better risk-adjusted returns?

MFSB currently has the higher Sharpe Ratio (1.59 vs 1.42), 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.