Merck & Co., Inc.
MX ˙ BMV ˙ US58933Y1055
SecurityMX:MRK / Merck & Co., Inc.
InstitutionMain Street Research LLC
Latest Disclosed Ownership9,521 shares
Latest Disclosed Value $ 1,145,295
Main Street Research LLC reports 22.32% increase in ownership of MRK / Merck & Co., Inc.

On April 30, 2026 - Main Street Research LLC filed a 13F-HR form disclosing ownership of 9,521 shares of Merck & Co., Inc. (MX:MRK) valued at $1,145,295 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 9, 2026 disclosing 7,784 shares of Merck & Co., Inc.. This represents a change in shares of 22.32% during the quarter.

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.

Upgrade to unlock premium data and export to Excel .

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)
2026-04-30 2026-03-31 13F MERCK COM 58933Y105 9,521 1,737 22.32 1,145 38.79 0.0666
2026-02-09 2025-12-31 13F MERCK COM 58933Y105 7,784 -1,486 -16.03 826 6.04 0.0472
2025-11-13 2025-09-30 13F MERCK COM 58933Y105 9,270 302 3.37 778 8.51 0.0420
2025-08-05 2025-06-30 13F MERCK COM 58933Y105 8,968 -262 -2.84 717 -14.23 0.0446
2025-04-30 2025-03-31 13F MERCK COM 58933Y105 9,230 -437 -4.52 836 -13.73 0.0546
2025-02-07 2024-12-31 13F MERCK COM 58933Y105 9,667 -22 -0.23 970 -12.47 0.0604
2024-11-12 2024-09-30 13F MERCK COM 58933Y105 9,689 3,914 67.77 1,108 53.96 0.0697
2024-07-29 2024-06-30 13F MERCK COM 58933Y105 5,775 313 5.73 719 -0.69 0.0475
2024-05-01 2024-03-31 13F MERCK COM 58933Y105 5,462 -209 -3.69 725 -4.49 0.0493
2024-01-30 2023-12-31 13F MERCK COM 58933Y105 5,671 -101,637 -94.72 758 -93.19 0.0609
2023-11-03 2023-09-30 13F MERCK COM 58933Y105 107,308 -779 -0.72 11,126 -10.83 1.1462
2023-08-08 2023-06-30 13F MERCK COM 58933Y105 108,087 101,658 1,581.24 12,477 1,713.37 1.9885
2023-05-01 2023-03-31 13F MERCK COM 58933Y105 6,429 -316 -4.68 689 -8.63 0.1360
2023-02-06 2022-12-31 13F MERCK COM 58933Y105 6,745 374 5.87 753 37.16 0.1834
2022-11-14 2022-09-30 13F MERCK COM 58933Y105 6,371 1,510 31.06 549 23.93 0.1209
2022-08-12 2022-06-30 13F MERCK COM 58933Y105 4,861 -1,517 -23.78 443 -15.30 0.1161
2022-05-05 2022-03-31 13F MERCK COM 58933Y105 6,378 -946 -12.92 523 -6.77 0.0492
2022-02-09 2021-12-31 13F MERCK COM 58933Y105 7,324 1,126 18.17 561 20.39 0.0433
2021-11-12 2021-09-30 13F MERCK COM 58933Y105 6,198 400 6.90 466 3.33 0.0408
2021-08-06 2021-06-30 13F Merck COM 58933Y105 5,798 -250 -4.13 451 -3.22 0.0362
2021-05-07 2021-03-31 13F Merck COM 58933Y105 6,048 -1,306 -17.76 466 -22.59 0.0438
2021-02-12 2020-12-31 13F Merck COM 58933Y105 7,354 -458 -5.86 602 -7.10 0.0647
2020-11-10 2020-09-30 13F Merck COM 58933Y105 7,812 -1,350 -14.73 648 -8.60 0.0825
2020-07-29 2020-06-30 13F Merck COM 58933Y105 9,162 12 0.13 709 0.71 0.1113
2020-05-01 2020-03-31 13F Merck COM 58933Y105 9,150 -147,469 -94.16 704 -95.06 0.1725
2020-01-28 2019-12-31 13F Merck COM 58933Y105 156,619 -915 -0.58 14,244 7.41 2.2461
2019-10-21 2019-09-30 13F Merck COM 58933Y105 157,534 150,036 2,001.01 13,261 2,008.27 2.4874
2019-08-08 2019-06-30 13F Merck COM 58933Y105 7,498 458 6.51 629 7.34 0.1415
2019-05-13 2019-03-31 13F Merck COM 58933Y105 7,040 237 3.48 586 12.69 0.1863
2019-02-13 2018-12-31 13F Merck COM 58933Y105 6,803 -95 -1.38 520 6.34 0.2022
2018-11-05 2018-09-30 13F Merck COM 58933Y105 6,898 118 1.74 489 18.69 0.0702
2018-07-25 2018-06-30 13F Merck COM 58933Y105 6,780 -269 -3.82 412 7.29 0.0645
2018-05-08 2018-03-31 13F/A-1 Merck COM 58933Y105 7,049 -219 -3.01 384 -6.11 0.0608
2018-05-08 2018-03-31 13F Merck COM 58933Y105 7,268 0 409
2018-02-05 2017-12-31 13F Merck COM 58933Y105 7,268 -5,516 -43.15 409 -50.06 0.0623
2017-10-16 2017-09-30 13F Merck COM 58933Y105 12,784 -2,159 -14.45 819 -14.51 0.1322
2017-07-18 2017-06-30 13F Merck COM 58933Y105 14,943 -623 -4.00 958 -3.13 0.1565
2017-05-04 2017-03-31 13F Merck COM 58933Y105 15,566 -479 -2.99 989 4.66 0.1732
2017-02-03 2016-12-31 13F Merck COM 58933Y105 16,045 -185 -1.14 945 -6.71 0.1840
2016-11-10 2016-09-30 13F Merck COM 58933Y105 16,230 -300 -1.81 1,013 6.41 0.1980
2016-08-11 2016-06-30 13F Merck COM 58933Y105 16,530 0 0.00 952 8.80 0.1967
2016-05-13 2016-03-31 13F Merck COM 58933Y105 16,530 -165 -0.99 875 -0.79 0.2256
2016-02-04 2015-12-31 13F Merck COM 58933Y105 16,695 570 3.53 882 0.11 0.1885
2015-11-12 2015-09-30 13F Merck COM 58933Y105 16,125 1,449 9.87 881 5.38 0.2067
2015-07-23 2015-06-30 13F Merck COM 58933Y105 14,676 1,030 7.55 836 6.63 0.1712
2015-05-12 2015-03-31 13F Merck COM 58933Y105 13,646 583 4.46 784 5.66 0.1686
2015-02-09 2014-12-31 13F Merck COM 58933Y105 13,063 -85 -0.65 742 -4.75 0.1589
2014-11-13 2014-09-30 13F Merck COM 58933Y105 13,148 218 1.69 779 4.14 0.1735
2014-08-11 2014-06-30 13F Merck COM 58933Y105 12,930 32 0.25 748 2.19 0.1764
2014-05-12 2014-03-31 13F Merck COM 58933Y105 12,898 1,185 10.12 732 24.91 0.1778
2014-02-06 2013-12-31 13F Merck COM 58933Y105 11,713 65 0.56 586 5.59 0.1463
2013-11-12 2013-09-30 13F Merck COM 58933Y105 11,648 -286 -2.40 555 0.18 0.1499
2013-08-01 2013-06-30 13F Merck COM 58933Y105 11,934 11,934 554 0.1673
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.