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Note 12 - Retirement Benefit Plans | 6 Months Ended
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Jun. 30, 2025
Notes to Financial Statements |
Retirement Benefits [Text Block] | Note 12 — Retirement Benefit Plans We operate defined contribution retirement benefit plans and defined benefit pension plans. Our primary defined benefit pension plan is the defined benefit section of the Janus Henderson Group UK Pension Scheme (“JHGPS”). Net Periodic Benefit Cost The components of net periodic benefit cost in respect of defined benefit plans for the three and six months ended June 30, 2025 and 2024, include the following (in millions):
|  | Three months ended |  |  | Six months ended |
|  | June 30, |  |  | June 30, |
|  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Interest cost |  | $ | (8.7 | ) |  | $ | (6.7 | ) |  | $ | (16.5 | ) |  | $ | (13.5 | )
Amortization of prior service cost |  |  | (0.1 | ) |  |  | (0.1 | ) |  |  | (0.2 | ) |  |  | (0.2 | )
Amortization of net gain |  |  | (0.6 | ) |  |  | (0.3 | ) |  |  | (1.1 | ) |  |  | (0.6 | )
Expected return on plan assets |  |  | 8.7 |  |  |  | 6.5 |  |  |  | 16.4 |  |  |  | 13.4 |
Net periodic benefit cost |  | $ | (0.7 | ) |  | $ | (0.6 | ) |  | $ | (1.4 | ) |  | $ | (0.9 | )

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