Merck & Co., Inc.
MX ˙ BMV ˙ US58933Y1055
SecurityMX:MRK / Merck & Co., Inc.
InstitutionCalamos Advisors LLC
Latest Disclosed Ownership777,663 shares
Latest Disclosed Value $ 93,545,082
Calamos Advisors LLC ownership in MRK / Merck & Co., Inc.

On May 4, 2026 - Calamos Advisors LLC filed a 13F-HR form disclosing ownership of 777,663 shares of Merck & Co., Inc. (MX:MRK) valued at $93,545,082 USD as of March 31, 2026. The entity filed a previous 13F-HR on January 29, 2026 disclosing 719,806 shares of Merck & Co., Inc.. This represents a change in shares of 8.04% during the quarter.

Calamos Advisors LLC has a history of taking positions in derivatives of the underlying security (MRK) in the form of stock options. The firm currently holds call options representing 54,000 of underlying shares valued at $5,684,040 USD and put options representing 0 of underlying shares valued at $0 USD .

Note: prior versions of this page mistakenly stated that the share values represented the number of options, not the number of underlying shares. For more information on the data backing these reports, please see the SEC document Frequently Asked Questions About Form 13F.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Institutional Put/Call Ratios
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In addition to reporting standard equity and debt issues, institutions with more than 100MM assets under management must also disclose their put and call option holdings. Since put options generally indicate negative sentiment, and call options indicate positive sentiment, we can get a sense of the overall institutional sentiment by plotting the ratio of puts to calls. The chart to the right plots the historical put/call ratio for this instrument.

Using Put/Call Ratio as an indicator of investor sentiment overcomes one of the key deficiencies of using total institutional ownership, which is that a significant amount of assets under management are invested passively to track indices. Passively-managed funds do not typically buy options, so the put/call ratio indicator more closely tracks the sentiment of actively-managed funds.

MX:MRK / Merck & Co., Inc. Historical Put/Call Ratio
Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date
Effective
Date
Form Security Class ID Avg Price
Paid (Est)
Reported
Shares
ΔShares ΔShares
(%)
Reported
Value
(x1000)
ΔValue
(%)
Alloc
(%)
ΔAlloc ΔAlloc (%) Cost Basis
(x1000)
Unrealized
Gain/Loss
(x1000)
2026-05-04 2026-03-31 13F MERCK COM 58933Y105 777,663 57,857 8.04 93,545 23.47 0.3299
2026-01-29 2025-12-31 13F MERCK COM 58933Y105 719,806 209,606 41.08 75,767 76.94 0.2846
2025-10-20 2025-09-30 13F MERCK COM 58933Y105 510,200 -13 -0.00 42,821 6.02 0.1582
2025-08-08 2025-06-30 13F MERCK COM 58933Y105 510,213 -158,002 -23.65 40,388 -32.66 0.1590
2025-04-29 2025-03-31 13F MERCK COM 58933Y105 668,215 -184,632 -21.65 59,979 -29.31 0.2611
2025-01-24 2024-12-31 13F MERCK COM 58933Y105 852,847 -100,857 -10.58 84,841 -21.66 0.3548
2024-11-07 2024-09-30 13F MERCK COM 58933Y105 953,704 19,291 2.06 108,303 -6.38 0.4683
2024-07-25 2024-06-30 13F MERCK COM 58933Y105 934,413 -63,036 -6.32 115,680 -12.11 0.5138
2024-05-08 2024-03-31 13F MERCK COM 58933Y105 997,449 56,176 5.97 131,613 28.26 0.6235
2024-01-31 2023-12-31 13F MERCK COM 58933Y105 941,273 -29,334 -3.02 102,618 2.70 0.4977
2023-10-26 2023-09-30 13F MERCK COM 58933Y105 970,607 188,466 24.10 99,924 10.72 0.5191
2023-07-28 2023-06-30 13F MERCK COM 58933Y105 782,141 68,896 9.66 90,251 18.94 0.4465
2023-05-04 2023-03-31 13F MERCK COM 58933Y105 713,245 -60,622 -7.83 75,882 -11.62 0.3706
2023-01-26 2022-12-31 13F MERCK COM 58933Y105 773,867 -37,721 -4.65 85,861 22.84 0.4028
2022-10-24 2022-09-30 13F MERCK COM 58933Y105 811,588 162,388 25.01 69,894 18.09 0.3197
2022-08-01 2022-06-30 13F MERCK COM 58933Y105 649,200 17,920 2.84 59,188 14.27 0.2553
2022-05-03 2022-03-31 13F MERCK COM 58933Y105 631,280 -167,898 -21.01 51,797 -15.43 0.1945
2022-02-01 2021-12-31 13F MERCK COM 58933Y105 799,178 -10,590 -1.31 61,249 0.70 0.2290
2021-10-26 2021-09-30 13F MERCK COM 58933Y105 809,768 50,329 6.63 60,822 2.98 0.2656
2021-07-22 2021-06-30 13F MERCK COM 58933Y105 759,439 115,257 17.89 59,062 18.93 0.2698
2021-04-12 2021-03-31 13F MERCK & CO. COM 58933Y105 644,182 12,048 1.91 49,660 -3.96 0.2709
2021-01-27 2020-12-31 13F MERCK & CO. COM 58933Y105 632,134 -17,014 -2.62 51,709 -3.97 0.3001
2020-10-26 2020-09-30 13F MERCK & CO. COM 58933Y105 649,148 -36,281 -5.29 53,847 1.59 0.3466
2020-07-27 2020-06-30 13F MERCK & CO. COM 58933Y105 685,429 -95,318 -12.21 53,004 -11.76 0.3747
2020-04-28 2020-03-31 13F MERCK & CO. COM 58933Y105 780,747 -383,098 -32.92 60,071 -43.25 0.4714
2020-01-15 2019-12-31 13F MERCK COMMON STOCK 58933Y105 1,163,845 -8,267 -0.71 105,852 7.28 0.5234
2019-10-21 2019-09-30 13F MERCK COMMON STOCK 58933Y105 1,172,112 42,846 3.79 98,668 4.20 0.5374
2019-08-07 2019-06-30 13F MERCK COMMON STOCK 58933Y105 1,129,266 112,547 11.07 94,689 11.98 0.5257
2019-04-12 2019-03-31 13F MERCK COMMON STOCK 58933Y105 1,016,719 95,568 10.37 84,561 20.14 0.5276
2019-01-24 2018-12-31 13F MERCK COMMON STOCK 58933Y105 921,151 63,712 7.43 70,385 15.71 0.4646
2018-10-22 2018-09-30 13F MERCK COMMON STOCK 58933Y105 857,439 -9,454 -1.09 60,827 15.60 0.3346
2018-07-17 2018-06-30 13F MERCK COMMON STOCK 58933Y105 866,893 -24,749 -2.78 52,620 8.34 0.3216
2018-04-13 2018-03-31 13F MERCK COMMON STOCK 58933Y105 891,642 -61,279 -6.43 48,568 -9.42 0.3160
2018-02-13 2017-12-31 13F MERCK COMMON STOCK 58933Y105 952,921 -198,877 -17.27 53,621 -27.29 0.2733
2017-10-25 2017-09-30 13F MERCK COMMON STOCK 58933Y105 1,151,798 -107,402 -8.53 73,750 -8.61 0.5703
2017-08-09 2017-06-30 13F MERCK COMMON STOCK 58933Y105 1,259,200 1,375 0.11 80,702 0.98 0.5965
2017-04-20 2017-03-31 13F MERCK COMMON STOCK 58933Y105 1,257,825 -12,778 -1.01 79,922 6.85 0.6293
2017-02-06 2016-12-31 13F MERCK COMMON STOCK 58933Y105 1,270,603 -13,662 -1.06 74,800 -6.68 0.5945
2016-11-14 2016-09-30 13F MERCK COMMON STOCK 58933Y105 1,284,265 -10,787 -0.83 80,151 7.43 0.5728
2016-07-26 2016-06-30 13F MERCK COMMON STOCK 58933Y105 1,295,052 -350,687 -21.31 74,608 -14.32 0.5234
2016-04-25 2016-03-31 13F MERCK COMMON STOCK 58933Y105 1,645,739 24,206 1.49 87,076 1.67 0.5777
2016-02-05 2015-12-31 13F MERCK COMMON STOCK 58933Y105 1,621,533 -79,957 -4.70 85,649 1.92 0.5442
2015-11-10 2015-09-30 13F MERCK COMMON STOCK 58933Y105 1,701,490 35,327 2.12 84,037 -11.40 0.5791
2015-08-14 2015-06-30 13F MERCK COMMON STOCK 58933Y105 1,666,163 568,088 51.73 94,855 50.28 0.5859
2015-05-13 2015-03-31 13F MERCK COMMON STOCK 58933Y105 1,098,075 -19,285 -1.73 63,117 -0.53 0.3956
2015-02-13 2014-12-31 13F MERCK COMMON STOCK 58933Y105 1,117,360 -7,633 -0.68 63,455 -4.85 0.4197
2014-11-14 2014-09-30 13F MERCK COMMON STOCK 58933Y105 1,124,993 -416 -0.04 66,690 2.43 0.4451
2014-08-14 2014-06-30 13F MERCK COMMON STOCK 58933Y105 1,125,409 25,457 2.31 65,105 4.26 0.4126
2014-05-16 2014-03-31 13F MERCK COMMON STOCK 58933Y105 1,099,952 -2,493 -0.23 62,444 13.17 0.3991
2014-02-14 2013-12-31 13F MERCK COMMON STOCK 58933Y105 1,102,445 -768,616 -41.08 55,177 -38.06 0.3508
2013-11-14 2013-09-30 13F MERCK COMMON STOCK 58933Y105 1,871,061 -79,825 -4.09 89,081 -1.70 0.5587
2013-08-12 2013-06-30 13F MERCK COMMON STOCK 58933Y105 1,950,886 1,950,886 90,619 0.5922
Disclosed Call Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share
Price
Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2026-05-04 2026-03-31 13F MERCK COM Call 54,000 -10.00 5,684 12.89 n/a n/a n/a
2026-01-29 2025-12-31 13F MERCK COM Call 60,000 5,036 n/a n/a n/a
2025-10-20 2025-09-30 13F MERCK COM Call 0 -100.00 0 -100.00 n/a n/a n/a
2025-08-08 2025-06-30 13F MERCK COM Call 41,000 3,680 n/a n/a n/a
2024-01-31 2023-12-31 13F MERCK COM Call 0 -100.00 0 -100.00 n/a n/a n/a
2023-10-26 2023-09-30 13F MERCK COM Call 30,500 3,519 n/a n/a n/a
Disclosed Put Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share Price Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2024-07-25 2024-06-30 13F MERCK COM Put 0 -100.00 0 -100.00 n/a n/a n/a
2024-05-08 2024-03-31 13F MERCK COM Put 70,000 7,631 n/a n/a n/a
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.