Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations (continued)
Marketing and sales expense
Marketing and sales expense was $121,244 and $94,594 for the three months ended September 30, 2023, and 2022, respectively. This was an increase of 28.2%. Compensation and benefits expense increased $23,413 during the three months ended September 30, 2023 compared to the same period in 2022. Marketing and sales expense was $358,058 and $284,922 for the nine months ended September 30, 2023, and 2022, respectively. This was an increase of 25.7%. Compensation expense and travel expense increased $51,411 and $17,399, respectively, during the nine months ended September 30, 2023 compared to the same period in 2022. We increased our sales staff and exhibited at additional international photonics trade shows during 2023.
Stock compensation expense
Included in total expenses were noncash stock-based compensation costs of $0 and $8,670 for the three months ended September 30, 2023 and 2022, respectively, and $45,485 and $40,642 for the nine months ended September 30, 2023 and 2022, respectively. Compensation expense for all stock-based awards is based on the grant date fair value and recognized over the required service (vesting) period. There was no unrecognized non-cash stock-based compensation expense at September 30, 2023.
Interest
Interest income, net was $81,252, and $194,143 for the three and nine months ended September 30, 2023, respectively. Interest income, net was $363 for the three months ended September 30, 2023 and interest expense, net was $11,899 for the nine months ended September 30, 2022. The improvement was due to our increase in cash and approximately $2.0 million of investments in marketable securities which benefited from an overall increase in interest rates. Interest expense has decreased as we continue to reduce our debt outstanding.
Income taxes
Income tax expense was $212,677, and $167,375 for the three months ended September 30, 2023, and 2022, respectively. Income tax expense was $515,233, and $311,575 for the nine months ended September 30, 2023, and 2022, respectively. The effective tax rate for the nine months ended September 30, 2023 was 24.0%, compared to the tax rate of 21.7% for calendar year 2022. At December 31, 2022, the deferred tax asset was $151,164. As of each reporting date, management considers new evidence, both positive and negative, that could affect its view of the future realization of deferred tax assets. Accordingly, management determined that no valuation allowance was necessary at December 31, 2022. The deferred tax asset was $0, and the deferred tax liability was $215,967 at September 30, 2023.
Net income
Net income for the three months ended September 30, 2023, and 2022, was $578,784 and $442,703, respectively. Net income for the nine months ended September 30, 2023, and 2022, was $1,628,163, and $1,491,977, respectively. The increase was the result of higher revenue and gross profit.
Liquidity and Capital Resources
Cash and cash equivalents
As of September 30, 2023, cash on hand was $5,798,613 compared to $3,947,966 at December 31, 2022. The increase was due to net cash provided by operating activities partially offset by investment in our manufacturing footprint and acquisition of production equipment.
Working capital
At September 30, 2023, working capital was $7,139,370 compared to $5,211,625 at December 31, 2022, an increase of $1,927,745 or 37.0%. Cash increased $1,850,647, accounts receivable-trade increased $376,179, inventories increased $1,009,304, prepaid purchase orders increased $1,171,740 and customer deposits increased $2,410,832.