In a recent article, we examined the growth of Medicare Advantage (MA) and considered potential policy impacts as it overtakes Traditional Medicare in percentage of enrollees covered. To continue that effort, we examined MA enrollment at the county level and forecasted enrollment trends county-by-county over the 12-month period from February 2023 to January 2024. Our results show that MA continues to overtake Fee-for-Service enrollment, with 34.4% of counties predicted to have MA penetration rates of 50% or more by January 2024. We highlight the largest counties becoming majority MA and highlight large counties that are forecast to have the largest percent increases and decreases in MA penetration in 2024.

We utilized monthly Medicare Advantage State/County enrollment and eligibility data from January 2018 through January 2023 to forecast county-level Medicare eligibility, MA enrollment and MA penetration rates through January 2024 for the 50 U.S. states and the District of Columbia. To improve the accuracy of the forecast results, counties with a MA enrollment count of zero for any month between January 2018 and January 2023 were excluded from our forecast model. Using exponential smoothing forecast methods, we projected county-level MA enrollment and Medicare eligibility from February 2023 through January 2024. We then calculated county-level penetration rates based on the predicted MA enrollee count over the predicted Medicare eligible count.

Our forecast models resulted in a high degree of precision with an overall error (MAPE) of 0.014% for MA enrollment counts and 0.002% for Medicare eligible counts. We calculated the MAPE at the county level for both MA enrolled and Medicare eligible counts. The county level MAPE on predicted Medicare eligibility counts was relatively small, ranging from -0.12% to 0.13%. County level MAPE values for Medicare enrollment counts ranged from -11.46% to 2.76%. For any counties with a MA enrolled count error of more than +/- 5% we utilized the January 2023 Medicare enrolled count in calculating the penetration rate for January 2024. We used this same technique for the 101 counties that were excluded from the forecast due to no MA enrollment in any month in our timeframe as well as 34 counties for which the forecast predicted negative MA enrollment counts for January 2024.

We assigned counties Metropolitan Statistical Area (MSA) values to distinguish urban/rural areas. Our forecast model was better at predicting MA enrollment in urban compared to rural areas, with MAPE values for MA enrollment counts of -0.008% and -0.016%, respectively. At the state level, states with the greatest MAPE were Wyoming (- 0.36%), Utah (-0.39%) and Nevada (-0.90%) while the best prediction occurred for Ohio (-0.00004%) and New York (0.0007%).

By January 2024, our models predict that 34.4% of counties will have MA penetration rates at or above 50% compared to just 6.4% of counties in January 2018, the start of our analysis timeframe.

Forecasted Yearly Medicare Advantage Enrollment

Table 1. Ten Counties with Greatest Projected Increases in Penetration Rates from January 2023 to January 2024

State Name County Name January 2023
Actual MA Penetration
January 2024
Projected MA Penetration
Michigan Ingham 61.6% 69.1% 7.4%
California San Bernardino 57.5% 62.5% 5.0%
Texas Galveston 52.1% 56.5% 4.4%
Connecticut Hartford 55.0% 59.3% 4.3%
Connecticut New London 46.7% 50.9% 4.2%
Connecticut New Haven 51.2% 55.3% 4.1%
California Riverside 55.7% 59.7% 4.0%
Massachusetts Bristol 32.9% 36.8% 3.9%
Iowa Polk 40.0% 43.9% 3.8%
New Jersey Atlantic 38.4% 42.2% 3.8%

Note: Limited to counties with 50,000 or more Medicare eligibles as of January 1, 2023.

Penetration rate increases in counties with large Medicare eligible populations are shown in Table 1. Percentage decreases in penetration rates among counties with large eligible populations are as shown in Table 2 and were greatest in several Illinois and Florida counties, as well as Macomb County in Michigan and Honolulu County in Hawaii (See Table 2).

Table 2. Ten Counties with Largest Projected Decreases in Penetration Rates from January 2023 to January 2024

State Name County Name January 2023
Actual MA Penetration
January 2024
Projected MA Penetration
Illinois Winnebago 47.8% 15.1% -32.7%
Illinois Madison 44.7% 31.5% -13.2%
Illinois St. Clair 47.7% 38.2% -9.5%
Hawaii Honolulu 53.5% 48.4% -5.1%
Florida Charlotte 48.2% 43.3% -4.9%
Florida Osceola 69.3% 65.3% -4.0%
Illinois Mchenry 26.7% 23.3% -3.5%
Florida Lee 46.2% 42.8% -3.5%
Michigan Macomb 54.0% 51.0% -3.0%
Florida Volusia 57.9% 54.9% -2.9%

Note: Limited to counties with 50,000 or more Medicare eligibles as of January 1, 2023.

Based on our predicted penetration rates for January 2024, Table 3 shows the counties with the largest Medicare eligible populations expected to become majority MA in 2024. While these percentage increases are relatively small, they represent thousands of enrollees shifting to MA and the tipping of the balance within these counties to managed care.

Table 3. Ten Counties with Largest Medicare-Eligible Population that Will Become Majority MA in 2024.

State Name County Name January 2023
Actual MA Penetration
January 2024
Projected MA Penetration
Arizona Maricopa 50.0% 51.0%
Washington King 48.9% 50.1%
Florida Duval 49.6% 51.3%
North Carolina Wake 47.8% 51.3%
Kentucky Jefferson 47.6% 50.1%
Oklahoma Tulsa 48.0% 50.2%
Colorado El Paso 47.2% 50.2%
Pennsylvania Lancaster 48.7% 50.3%
Texas Montgomery 49.4% 50.7%
Pennsylvania York 48.8% 50.9%

The penetration rate used in our analysis represents the percent of total Medicare eligibles, and is not restricted to those who are enrolled in both Part A and Part B. As noted in an analysis by Trish et al recently published in Health Affairs, this penetration rate does underestimate the actual take-up of MA slightly because it includes enrollees who only have Part A coverage and therefore, are not eligible to enroll in MA. We have utilized this penetration rate in order to include more recent data, specifically January 2023 enrollment data, which does not include counts of Medicare Part A and B enrollees.

We anticipate continued growth in MA; however, it will be intriguing to observe how future growth projections shift due to factors such as the Centers for Medicare & Medicaid's (CMS) payment model adjustments, the finalization of CMS' Risk Adjustment Data Validation (RADV) audit methodology and overpayment collection, probable efforts by the Health and Human Services Office of the Inspector General (HHS OIG) to detect and recover overpayments from MA plans, and the effects of recent modifications to CMS' Medicare Star ratings.

As part of our mission to provide actionable insights to healthcare payers, Magpie Health Analytics is releasing this series of articles that projects future MA growth at the national and county level, giving invaluable perspectives into the market-level impacts of the changing MA landscape. Sign up to receive future articles in this series and other insightful articles on health care topics.