6. Property and Equipment, Net

The balances of the major classes of property and equipment are as follows (in thousands):

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Depreciation of fixed assets, including the amortization of capitalized software, for the three months ended September 30, 2024 and 2023 was $21.1 million and $3.9 million, respectively. Depreciation of fixed assets, including the amortization of capitalized software, for the nine months ended September 30, 2024 and 2023 was $31.4 million and $11.4 million, respectively.

We capitalized $4.3 million and $12.1 million in software development costs for the three and nine months ended September 30, 2024, respectively. Amortization of capitalized software was $2.7 million and $1.3 million for the three months ended September 30, 2024 and 2023, respectively, and was $7.4 million and $3.8 million for the nine months ended September 30, 2024 and 2023, respectively. The net book value of capitalized software development costs was $28.1 million and $23.4 million as of September 30, 2024 and December 31, 2023, respectively.

There were no impairments of property and equipment for the three and nine months ended September 30, 2024 and 2023, respectively. Due to the relocation of one of our office locations, we reduced the useful life of the related finance lease and leasehold improvement assets which represented $15.8 million of incremental depreciation for the three and nine months ended September 30, 2024. The remaining net book value of the aforementioned assets as of September 30, 2024 is $2.1 million, which will fully depreciate in the fourth quarter of 2024.