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PENSION PLANS AND RETIREMENT BENEFITS | 9 Months Ended
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Sep. 30, 2025
Retirement Benefits [Abstract] |
PENSION PLANS AND RETIREMENT BENEFITS | NOTE 11. PENSION PLANS AND RETIREMENT BENEFITS We sponsor domestic and foreign defined benefit pension plans for eligible employees and retirees. Most of our domestic employees participate in defined contribution plans. However, a portion of our bargaining hourly employees continue to participate in our domestic qualified defined benefit pension plans under a flat-benefit formula. Our funding policy for the qualified defined benefit pension plans is consistent with the requirements of federal laws and regulations. Our foreign subsidiaries maintain pension and other benefit plans, which are consistent with local statutory practices. Our domestic qualified defined benefit pension plan provides that if, within three years following a change of control of Olin, any corporate action is taken or filing made in contemplation of, among other things, a plan termination or merger or other transfer of assets or liabilities of the plan, and such termination, merger, or transfer thereafter takes place, plan benefits would automatically be increased for affected participants (and retired participants) to absorb any plan surplus (subject to applicable collective bargaining requirements). We also provide certain postretirement healthcare (medical) and life insurance benefits for eligible active and retired domestic employees. The healthcare plans are contributory with participants’ contributions adjusted annually based on medical rates of inflation and plan experience.
| Pension Benefits |  | Other Postretirement Benefits
| Three Months Ended September 30, |  | Three Months Ended September 30,
| 2025 |  | 2024 |  | 2025 |  | 2024
Components of Net Periodic Benefit (Income) Cost | ($ in millions)
Service cost | $ | 1.3 |  |  | $ | 1.4 |  |  | $ | 0.1 |  |  | $ | — |
Interest cost | 24.9 |  |  | 25.5 |  |  | 0.4 |  |  | 0.2 |
Expected return on plans’ assets | (31.7) |  |  | (33.5) |  |  | — |  |  | — |
Amortization of prior service cost | (0.2) |  |  | (0.2) |  |  | 0.3 |  |  | (0.2) |
Recognized actuarial loss (gain) | 1.4 |  |  | 1.6 |  |  | — |  |  | (0.1) |
Net periodic benefit (income) cost | $ | (4.3) |  |  | $ | (5.2) |  |  | $ | 0.8 |  |  | $ | (0.1) |
| Pension Benefits |  | Other Postretirement Benefits
| Nine Months Ended September 30, |  | Nine Months Ended September 30,
| 2025 |  | 2024 |  | 2025 |  | 2024
Components of Net Periodic Benefit (Income) Cost | ($ in millions)
Service cost | $ | 3.5 |  |  | $ | 3.9 |  |  | $ | 0.4 |  |  | $ | 0.4 |
Interest cost | 74.3 |  |  | 76.1 |  |  | 1.1 |  |  | 1.1 |
Expected return on plans’ assets | (95.1) |  |  | (101.2) |  |  | — |  |  | — |
Amortization of prior service cost | (0.5) |  |  | (0.5) |  |  | 0.1 |  |  | (0.2) |
Recognized actuarial loss | 4.4 |  |  | 4.9 |  |  | 0.2 |  |  | 0.4 |
Net periodic benefit (income) cost | $ | (13.4) |  |  | $ | (16.8) |  |  | $ | 1.8 |  |  | $ | 1.7 |
We made cash contributions to our international qualified defined benefit pension plans of $0.6 million and $0.9 million for the nine months ended September 30, 2025 and 2024, respectively.

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