Fund Evaluator:
MFS Core Bond R4 (MCBKX)
Follow This Fund
Best Performing in Intermediate Core Bond Over the Last Year
| 4.5% | Aristotle Pacific EXclusive Series I (APXIX) |
| 4.0% | MML Barings Core Bond M1 (MMCDX) |
| 3.9% | MML Barings Core Bond M2 (MMCAX) |
| 3.2% | Nuveen Core and Impact Bond I (TSBHX) |
| 3.1% | American Beacon DoubleLine Sel Inc Inv (BILTX) |
Fund Details
MFS Core Bond R4 Overview
MFS Core Bond R4 (MCBKX) is an actively managed Taxable Bond Intermediate Core Bond fund. MFS launched the fund in 2022.
The investment seeks total return with an emphasis on current income, but also considering capital appreciation. The fund normally invests at least 80% of the fund’s net assets in investment grade quality debt instruments. Debt instruments include corporate debt instruments, U.S. government securities, securitized instruments (including mortgage-backed securities and other asset-backed securities), and other obligations to repay money borrowed.
About MFS Core Bond R4 (MCBKX)
There are 3 members of the management team with an average tenure of 2.85 years: Joshua Marston (2022), Alexander Mackey (2022), Philipp Burgener (2026). Management tenure is more important for actively managed funds than passive index funds.
The fund has 1 primary benchmark: Bloomberg US Agg Bond TR USD index with a weighting of 100%. MFS Core Bond R4 has 319 securities in its portfolio. The top 10 holdings constitute 31.2% of the fund’s assets. The fund meets the SEC requirement of being classified as a diversified fund. The fund is not considered to have an ESG focus with its investment selection and management.
MFS Core Bond R4 is part of the Fixed Income global asset class and is within the Taxable Bond fund group. MFS Core Bond R4 has 13.1% of its portfolio invested in foreign issues. The overall assets allocated to domestic stock is 0.0%. There is 0.0% allocated to foreign stock, and 0.1% is allocated to preferred stocks. The bond allocation as a percentage of total assets is 116.6% (103.5% domestic bond, 13.1% foreign bond and 0.0% convertible bond). MFS Core Bond R4 has -16.7% of the portfolio in cash.
Assets Under Management
The fund has $56 million in total assets, which is below the $3 billion average for the Intermediate Core Bond category. Normally, lower assets under management translates to higher average expense ratios, and greater total assets are desired. However, for some investment categories, such as small-cap investing, it may be difficult for the manager to fully employ the desired active strategy if assets grow too large or too quickly.
MCBKX Performance and Fees
The expense ratio measures how much of a fund’s assets are used for administrative expenses and operating expenses, including adviser fees and fees for the transfer agent and custodial services. The MFS Core Bond R4 expense ratio is below average compared to funds in the Intermediate Core Bond category. MFS Core Bond R4 has an expense ratio of 0.39%, which is 31% lower than its category average, making the fund expense ratio grade a B. While it is difficult to predict returns, it is known that high annual expense ratios reduce your rate of return, and excessive fees are difficult to overcome. Active management normally comes with higher expense ratios than passive index management. Certain investment categories such as small company and foreign also normally have higher expense ratios. It is best to compare fund expense ratios against the category averages for meaningful assessments.
High portfolio turnover can translate to higher expenses and lower aftertax returns. MFS Core Bond R4 has a portfolio turnover rate of 110%, indicating that holds its assets around 0.0 years. By way of comparison, the average portfolio turnover is 151% for the Intermediate Core Bond category.
Recently, in the month of July 2026, MFS Core Bond R4 returned -1.3%, which earned it a grade of B, as the Intermediate Core Bond category had an average return of -1.3%. The letter grades of A, B, C, D and F are based upon relative rankings within the investment category. A grade of A, for example, would indicate that the return is in the highest 20% for that time period compared to all funds in that category.
MFS Core Bond R4 has a trailing yield of 4.73%, which is above the 4.04% category average. The fund normally distributes its income monthly and its capital gains annually.
It’s natural to seek the best-performing investments, but you must consider the relationship between risk and return and the impact of costs and taxes on your realized returns.
MFS Core Bond R4 Grades
Year to date, the fund has returned -0.5%, 0.2 percentage points better than the category, which translates into a grade of B. The fund has returned 2.7% over the past year (grade of B) and 3.9% over the past three years (grade of B).
For more mutual fund grades, analysis and screening tools to help your investment discovery, join AAII for a $2, full-access trial. Learn more here: https://invest.aaii.com/membership.
Otherwise, for more information about MFS Core Bond R4, including its riskiness, submit your email to unlock the rest of the article.
Gain access to exclusive AAII member-only content.
MCBKX Trailing NAV Total Returns Data as of 7/31/26
| Last Month |
Last Quarter |
Ann'l. 1Yr |
Ann'l. 3Yr |
Ann'l. 5Yr |
Ann'l. 10Yr |
|
| MCBKX Return (NAV) | -1.3% | -0.7% | 2.7% | 3.9% | na | na |
| MCBKX Grade | B | A | B | B | na | na |
| +/- Category | 0.0% | 0.1% | 0.2% | 0.2% | na | na |
| Intermediate Core Bond Avg | -1.3% | -0.8% | 2.5% | 3.7% | -0.5% | 1.4% |
| MCBKX Tax Cost Ratio | na | na | 1.9% | 1.9% | na | na |
MCBKX Annual NAV Total ReturnsData as of 7/31/26
| 2026 | 2025 | 2024 | 2023 | 2022 | 2021 | 2020 | 2019 | 2018 | 2017 | 2016 | |
| MCBKX Return (NAV) | -0.5% | 7.2% | 1.8% | 6.4% | na | na | na | na | na | na | na |
| MCBKX Grade | B | C | B | A | na | na | na | na | na | na | na |
| +/- Category | 0.2% | 0.2% | 0.2% | 0.8% | na | na | na | na | na | na | na |
| Intermediate Core Bond Avg | -0.7% | 7.0% | 1.6% | 5.6% | -13.2% | -1.5% | 8.1% | 8.5% | -0.4% | 3.6% | 2.8% |
| Risk Measures | |
| Standard Deviation: | 5.6% |
| Total Risk Index: | 0.46 - Low |
| Category Risk Index: | 1.00 - Average |
| Category Risk Grade: | C (56% Rank) |
| Beta: | 1.00 |
| R-Squared: | 100% |
| Leveraged Fund: | No |
| Inverse Fund: | No |
| Portfolio Characteristics | |
| Equity Investment Style: | na |
| Bond Investment Style: | High Quality Moderate Sensitivity |
| Yield: | 4.7% |
| Dividend Distribution: | Monthly |
| Cap Gains Distribution: | Annually |
| Total Assets: | $34 Mil |
| Fund Total Assets: | $ 0 Mil |
| Share Class Type: | Retirement |
| Portfolio Turnover: | 110% |
Management Team
| Number of Managers: 3 | |||
| Longest Tenure: 4.1 years | |||
| Average Tenure: 2.9 years | |||
| Managers (Year): Marston Joshua (2022), Mackey Alexander (2022), Burgener Philipp (2026) | |||
Portfolio Composition (as of 6/30/26)
| # of Holdings: | 319 |
| % in Top 10 Holdings: | 31.2% |
| Fund is Non-Diversified: | No |
| % in Foreign Issues: | 13.1% |
Portfolio Allocation |
|
| Domestic Stock: | 0.0% |
| Foreign Stock: | 0.0% |
| Preferred Stock: | 0.1% |
| Domestic Bond: | 103.5% |
| Foreign Bond: | 13.1% |
| Convertible Bond: | 0.0% |
| Other: | 0.0% |
| Cash: | -16.7% |
Purchase Information
| Fund Family: | MFS |
| Phone Number: | 800-225-2606 |
| Website: | http://www.mfs.com |
| Status: | Open |
| Inception Date: | June 22, 2022 |
| Min. Initial Purchase: | $ 0 |
| Min. Initial IRA Purchase: | $ 0 |
| True No-Load: | Yes |
| Front Load Maximum: | 0.00% |
| Deferred Charge Maximum: | 0.00% |
| Redemption Charge Maximum: | 0.00% |
| 12b-1 Fee: | na |
Expenses and Fees | |
| Expense Ratio (%): | 0.39% ( Rating : Below Avg ) |
| Category Average Expense Ratio (%): | 0.57% |
| Share Class: | MFS Core Bond R6 |
| Min. Subsequent Purchase: | $ 0 |
| Min. Subsequent IRA Purchase: | $ 0 |
