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Components of Net Periodic Benefit Cost | 9 Months Ended
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Sep. 30, 2025
Components of Net Periodic Benefit Cost |
Components of Net Periodic Benefit Cost | 8. Components of Net Periodic Benefit Cost ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three Months Ended September 30, | ​ | Nine Months Ended September 30,
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | Post-Retirement | ​ | ​ | ​ | ​ | ​ | ​ | ​ | Post-Retirement
​ | ​ | Pension Benefits | ​ | Health Benefits | ​ | Pension Benefits | ​ | Health Benefits
(Dollar amounts in thousands) |  | 2025 |  | 2024 | ​ | 2025 |  | 2024 | ​ | 2025 |  | 2024 | ​ | 2025 |  | 2024
Service cost | ​ | $ | 108 | ​ | $ | 142 | ​ | $ | 3 | ​ | $ | 4 | ​ | $ | 323 | ​ | $ | 424 | ​ | $ | 9 | ​ | $ | 12
Interest cost | ​ |  | 1,016 | ​ |  | 947 | ​ |  | 32 | ​ |  | 34 | ​ |  | 3,049 | ​ |  | 2,841 | ​ |  | 96 | ​ |  | 103
Expected return on plan assets | ​ |  | (1,094) | ​ |  | (1,051) | ​ |  | — | ​ |  | — | ​ |  | (3,281) | ​ |  | (3,154) | ​ |  | — | ​ |  | —
Net amortization of prior service cost | ​ |  | — | ​ |  | — | ​ |  | — | ​ |  | — | ​ |  | — | ​ |  | — | ​ |  | — | ​ |  | —
Net amortization of net (gain) loss | ​ | ​ | — | ​ | ​ | 109 | ​ | ​ | (39) | ​ | ​ | (20) | ​ | ​ | — | ​ | ​ | 326 | ​ | ​ | (117) | ​ | ​ | (60)
Net Periodic Benefit Cost | ​ | $ | 30 | ​ | $ | 147 | ​ | $ | (4) | ​ | $ | 18 | ​ | $ | 91 | ​ | $ | 437 | ​ | $ | (12) | ​ | $ | 55
​ Employer Contributions First Financial Corporation previously disclosed in its financial statements for the year ended December 31, 2024 that it expected to contribute $570 thousand and $563 thousand respectively to its Pension Plan and ESOP and $243 thousand to the Post Retirement Health Benefits Plan in 2025. Contributions of $905 thousand have been made to the Pension Plan thus far in 2025. Contributions of $188 thousand have been made through the first nine months of 2025 for the Post Retirement Health Benefits plan. No contributions have been made in 2025 for the ESOP. The Pension plan was frozen for most employees at the end of 2012 and for those employees there will be discretionary contributions to the ESOP plan and a 401K plan in place of the former Pension benefit. In the first nine months of 2025 and 2024 there has been $2.4 million and $2.4 million of expense accrued for potential contributions to these alternative retirement benefit options.

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