Arthur J. Gallagher & Co.
MX ˙ BMV ˙ US3635761097
SecurityMX:AJG / Arthur J. Gallagher & Co.
InstitutionJanus Henderson Group Plc
Latest Disclosed Ownership1,970,990 shares
Latest Disclosed Value $ 426,886,844
Janus Henderson Group Plc reports 5.43% increase in ownership of AJG / Arthur J. Gallagher & Co.

On May 18, 2026 - Janus Henderson Group Plc filed a 13F-HR/A form disclosing ownership of 1,970,990 shares of Arthur J. Gallagher & Co. (MX:AJG) valued at $426,886,844 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 17, 2026 disclosing 1,869,559 shares of Arthur J. Gallagher & Co.. This represents a change in shares of 5.43% 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.

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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)
2026-05-18 2026-03-31 13F/A-1 GALLAGHER ARTHUR J COM 363576109 1,970,990 101,431 5.43 426,887 -11.78 0.0720
2026-05-15 2026-03-31 13F GALLAGHER ARTHUR J COM 363576109 1,970,990 101,431 5.43 426,887 -11.78 0.0792
2026-02-17 2025-12-31 13F GALLAGHER ARTHUR J COM 363576109 1,869,559 239,272 14.68 483,868 -4.21 0.2167
2025-11-14 2025-09-30 13F GALLAGHER ARTHUR J COM 363576109 1,630,287 81,996 5.30 505,124 1.94 0.2306
2025-08-14 2025-06-30 13F GALLAGHER ARTHUR J COM 363576109 1,548,291 17,916 1.17 495,519 -5.00 0.2429
2025-05-15 2025-03-31 13F GALLAGHER ARTHUR J COM 363576109 1,530,375 30,500 2.03 521,591 22.52 0.2859
2025-02-14 2024-12-31 13F GALLAGHER ARTHUR J COM 363576109 1,499,875 169,172 12.71 425,736 13.71 0.2164
2024-11-14 2024-09-30 13F GALLAGHER ARTHUR J COM 363576109 1,330,703 31,181 2.40 374,408 11.14 0.1916
2024-08-14 2024-06-30 13F GALLAGHER ARTHUR J COM 363576109 1,299,522 71,256 5.80 336,877 9.70 0.1804
2024-05-15 2024-03-31 13F GALLAGHER ARTHUR J COM 363576109 1,228,266 790,467 180.55 307,076 211.90 0.1675
2024-02-14 2023-12-31 13F GALLAGHER ARTHUR J COM 363576109 437,799 408,809 1,410.17 98,454 1,389.91 0.0587
2023-11-14 2023-09-30 13F GALLAGHER ARTHUR J COM 363576109 28,990 -1,677 -5.47 6,609 -1.86 0.0043
2023-08-14 2023-06-30 13F GALLAGHER ARTHUR J COM 363576109 30,667 -3,238 -9.55 6,734 3.86 0.0042
2023-05-15 2023-03-31 13F GALLAGHER ARTHUR J COM 363576109 33,905 -2,653 -7.26 6,483 -5.98 0.0043
2023-02-14 2022-12-31 13F GALLAGHER ARTHUR J COM 363576109 36,558 8,691 31.19 6,895 44.01 0.0049
2023-01-13 2022-09-30 13F/A-1 GALLAGHER ARTHUR J COM 363576109 27,867 -113 -0.40 4,788 4.91 0.0036
2022-11-14 2022-09-30 13F GALLAGHER ARTHUR J COM 363576109 27,867 -113 4,788 0.0036
2022-08-15 2022-06-30 13F GALLAGHER ARTHUR J COM 363576109 27,980 -120,780 -81.19 4,564 -82.43 0.0031
2022-05-16 2022-03-31 13F GALLAGHER ARTHUR J COM 363576109 148,760 44,984 43.35 25,974 47.51 0.0125
2022-02-14 2021-12-31 13F GALLAGHER ARTHUR J COM 363576109 103,776 23,384 29.09 17,608 47.36 0.0073
2021-11-16 2021-09-30 13F GALLAGHER ARTHUR J COM 363576109 80,392 -120,529 -59.99 11,949 -57.54 0.0052
2021-08-16 2021-06-30 13F GALLAGHER ARTHUR J COM 363576109 200,921 97,806 94.85 28,144 118.75 0.0120
2021-05-17 2021-03-31 13F GALLAGHER ARTHUR J COM 363576109 103,115 9,879 10.60 12,866 11.55 0.0059
2021-02-16 2020-12-31 13F GALLAGHER ARTHUR J COM 363576109 93,236 -158,325 -62.94 11,534 -56.57 0.0054
2020-11-16 2020-09-30 13F GALLAGHER ARTHUR J COM 363576109 251,561 16,795 7.15 26,557 16.04 0.0138
2020-08-14 2020-06-30 13F GALLAGHER ARTHUR J COM 363576109 234,766 -218,709 -48.23 22,887 -38.08 0.0128
2020-05-14 2020-03-31 13F GALLAGHER ARTHUR J COM 363576109 453,475 -278,475 -38.05 36,961 -46.97 0.0254
2020-02-18 2019-12-31 13F GALLAGHER ARTHUR J COM 363576109 731,950 -128,141 -14.90 69,703 -9.52 0.0357
2019-11-14 2019-09-30 13F GALLAGHER ARTHUR J COM 363576109 860,091 -120,546 -12.29 77,037 -10.31 0.0417
2019-07-31 2019-06-30 13F GALLAGHER ARTHUR J COM 363576109 980,637 -159,147 -13.96 85,893 -3.51 0.0468
2019-04-30 2019-03-31 13F GALLAGHER ARTHUR J COM 363576109 1,139,784 437,771 62.36 89,017 72.05 0.0493
2019-02-06 2018-12-31 13F GALLAGHER ARTHUR J COM 363576109 702,013 29,677 4.41 51,738 3.38 0.0330
2018-11-09 2018-09-30 13F GALLAGHER ARTHUR J COM 363576109 672,336 -131,895 -16.40 50,048 -4.67 0.0267
2018-08-10 2018-06-30 13F GALLAGHER ARTHUR J COM 363576109 804,231 -161,605 -16.73 52,500 -20.91 0.0299
2018-05-14 2018-03-31 13F GALLAGHER ARTHUR J COM 363576109 965,836 -318,961 -24.83 66,381 -18.35 0.0391
2018-03-12 2017-12-31 13F/A-1 GALLAGHER ARTHUR J COM 363576109 1,284,797 -501,445 -28.07 81,302 -26.05 0.0501
2018-02-09 2017-12-31 13F GALLAGHER ARTHUR J COM 363576109 1,284,797 -501,445 81,302
2017-11-14 2017-09-30 13F GALLAGHER ARTHUR J COM 363576109 1,786,242 -66,702 -3.60 109,943 3.64 0.0705
2017-08-17 2017-06-30 13F/A-1 GALLAGHER ARTHUR J COM 363576109 1,852,944 1,831,326 8,471.30 106,081 8,580.93 0.0723
2017-08-14 2017-06-30 13F GALLAGHER ARTHUR J COM 363576109 1,852,944 1,831,326 106,081
2017-05-03 2017-03-31 13F GALLAGHER ARTHUR J COM 363576109 21,618 900 4.34 1,222 13.46 0.0086
2017-01-30 2016-12-31 13F GALLAGHER ARTHUR J COM 363576109 20,718 2,400 13.10 1,077 15.56 0.0079
2016-10-24 2016-09-30 13F GALLAGHER ARTHUR J COM 363576109 18,318 0 0.00 932 6.88 0.0069
2016-07-29 2016-06-30 13F GALLAGHER ARTHUR J COM 363576109 18,318 0 0.00 872 6.99 0.0073
2016-05-12 2016-03-31 13F GALLAGHER ARTHUR J COM 363576109 18,318 0 0.00 815 8.67 0.0066
2016-02-03 2015-12-31 13F GALLAGHER ARTHUR J COM 363576109 18,318 0 0.00 750 -0.79 0.0060
2015-11-16 2015-09-30 13F GALLAGHER ARTHUR J COM 363576109 18,318 0 0.00 756 -12.70 0.0067
2015-08-17 2015-06-30 13F GALLAGHER ARTHUR J COM 363576109 18,318 13,641 291.66 866 295.43 0.0068
2015-06-02 2015-03-31 13F/A-1 GALLAGHER ARTHUR J COM 363576109 4,677 0 0.00 219 -0.45 0.0017
2015-05-15 2015-03-31 13F GALLAGHER ARTHUR J COM 363576109 4,677 219
2015-02-12 2014-12-31 13F GALLAGHER ARTHUR J COM 363576109 4,677 0 0.00 220 3.77 0.0016
2014-11-12 2014-09-30 13F GALLAGHER ARTHUR J COM 363576109 4,677 0 0.00 212 -2.75 0.0020
2014-08-13 2014-06-30 13F GALLAGHER ARTHUR J COM 363576109 4,677 0 0.00 218 -1.80 0.0020
2014-05-08 2014-03-31 13F GALLAGHER ARTHUR J COM 363576109 4,677 0 0.00 222 0.91 0.0022
2014-01-14 2013-12-31 13F GALLAGHER ARTHUR J COM 363576109 4,677 0 0.00 220 7.84 0.0022
2013-11-12 2013-09-30 13F GALLAGHER ARTHUR J COM 363576109 4,677 0 0.00 204 -1.45 0.0023
2013-08-15 2013-06-30 13F GALLAGHER ARTHUR J COM 363576109 4,677 4,677 207 0.0024
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.