SELLING, GENERAL AND ADMINISTRATIVE EXPENSES
As a percentage of revenue, selling, general and administrative expenses decreased from 26.3% for the three months ended June 30, 2024, to 22.8% for the three months ended June 30, 2025, and decreased from 26.2% for the six months ended June 30, 2024, to 21.6% for the six months ended June 30, 2025. Selling, general and administrative expenses as a percentage of revenue will generally fluctuate whenever there is a significant fluctuation in revenue for the periods being compared.
Selling, general and administrative expenses increased 1.7% from $59.4 million for the three months ended June 30, 2024, to $60.3 million for the three months ended June 30, 2025, and decreased 6.5% from $118.4 million for the six months ended June 30, 2024, to $110.6 million for the six months ended June 30, 2025. Selling, general and administrative expenses include personnel costs for management, accounting, information technology, human resources, sales and marketing, as well as independent auditor, tax and other professional fees, contract services and legal and litigation related costs. The increase in selling, general and administrative expenses for the three months ended June 30, 2025, compared to the three months ended June 30, 2024, was primarily due to a $4.0 million increase in professional and legal services partially offset by a $2.5 million decrease in amortization of intangible assets related to the Business Combination. The decrease for the six months ended June 30, 2025, compared to the six months ended June 30, 2024, was primarily attributable to the impact of the Business Efficiency Program, which was completed as of December 31, 2024 (other than our aim of selling our headquarters in Huntsville), resulting in decreased employee-related costs of $6.2 million and a $4.7 million decrease in amortization of intangible assets related to the Business Combination partially offset by a $3.9 million increase in professional and legal services. For the three and six months ended June 30, 2025, as compared to the three and six months ended June 30, 2024, changes in foreign currencies relative to the U.S dollar increased our selling, general and administrative expenses by approximately $1.2 million and $0.5 million, respectively.
RESEARCH AND DEVELOPMENT EXPENSES
As a percentage of revenue, research and development expenses decreased from 26.7% for the three months ended June 30, 2024, to 19.6% for the three months ended June 30, 2025, and decreased from 26.7% for the six months ended June 30, 2024, to 19.6% for the six months ended June 30, 2025. Research and development expenses as a percentage of revenue will generally fluctuate whenever there are incremental product development activities or significant fluctuations in revenue for the periods being compared.
Research and development expenses decreased 14.0% from $60.4 million for the three months ended June 30, 2024, to $51.9 million for the three months ended June 30, 2025, and decreased 16.4% from $120.6 million for the six months ended June 30, 2024, to $100.8 million for the six months ended June 30, 2025. The decrease in research and development expenses for the three months ended June 30, 2025, was primarily attributable to the impact of the Business Efficiency Program, which was completed as of December 31, 2024 (other than our aim of selling our headquarters in Huntsville), resulting in a reduction of employee-related costs of $6.3 million. The decrease for the six months ended June 30, 2025, was primarily attributable to the impact of the Business Efficiency Program which was completed as of December 31, 2024 resulting in a reduction of employee-related costs of $15.4 million. For the three and six months ended June 30, 2025 as compared to the three and six months ended June 30, 2024, changes in foreign currencies relative to the U.S. dollar increased our research and development expenses by approximately $1.1 million and $0.7 million, respectively.
Adtran Networks has arrangements with governmental entities for the purpose of obtaining funding for research and development activities. The Company classifies government grants received under these arrangements as a reduction to research and development expenses incurred. For the three months ended June 30, 2025 and 2024, the Company recognized $3.1 million and $2.2 million as a reduction of research and development expense, respectively. For the six months ended June 30, 2025 and 2024, the Company recognized $5.3 million and $4.1 million as a reduction of research and development expense, respectively.
We expect to continue to incur research and development expenses in connection with our new and existing products. We continually evaluate new product opportunities and engage in significant research and product development efforts, which provides for new product development, enhancement of existing products and product cost reductions. We may incur significant research and development expenses prior to the receipt of revenue from a major new product group.
GOODWILL IMPAIRMENT
No goodwill impairment was recognized during the three and six months ended June 30, 2025, and for the three months ended June 30, 2024. During the first quarter of 2024, qualitative factors such as a decrease in the Company’s market capitalization, cautious service provider spending due to economic uncertainty and continued customer focus on inventory adjustments, triggered a quantitative impairment assessment for our reporting units for goodwill and long-lived assets. The Company determined upon its quantitative impairment assessment to recognize a $297.4 million non-cash goodwill impairment charge for the Network Solutions reporting unit during the six months ended June 30, 2024. For additional information, see Note 8 of Notes to Condensed Consolidated Financial Statements included in Part I, Item 1 of this report.
INTEREST AND DIVIDEND INCOME
Interest and dividend income decreased from $0.4 million for the three months ended June 30, 2024, to $0.2 million for the three months ended June 30, 2025 and decreased from $0.8 million for the six months ended June 30, 2024, to $0.3 million for the six months ended