The average return credit is calculated by dividing the actual shock credits issued by the actual number of trodes returned. A variance in the assumed return rate compared to the actual rate would impact the estimate and potentially understate net sales (overestimated rate) or overstate net sales (underestimated rate) in any given year and create a corresponding misstatement of the liability due to customers.
As of September 30, 2024, the estimated value of our Therapeutic Device customer contract liability was $553. If the expected return rate had increased by 2%, the effect on current year’s reduction in sales and customer liability would have been approximately $90.
Results of Consolidated Operations
Our results of operations for the three and nine months ended September 30, 2024 and 2023 are as follows:
Revenue
Revenue for the three months ended September 30, 2024 was $6,997, compared to $6,347 for the three months ended September 30, 2023, an increase of $650, or 10%. Revenue for the nine months ended September 30, 2024 was $19,390, compared to $17,849 for the nine months ended September 30, 2023, an increase of $1,541, or 9%.
The increase in sales for the three months ended September 30, 2024, was primarily due to growth in both consumables and capital sales in our existing PulseVet® products, as well as growth in TRUFORMA® products, including the impact of launching new assays during the comparative period. The increase in sales for the nine months ended September 30, 2024, was primarily due to growth in both consumables and capital sales in our PulseVet® products, as well as growth in TRUFORMA® products, partially attributable to the launch of new assays during the comparative period, and the continued performance of VetGuardian®, which had only recently launched during the nine months ended September 30, 2023. In general, we expect revenue to increase in subsequent periods as we increase our sales, marketing, and commercialization efforts.
Cost of Revenue
Cost of revenue for the three months ended September 30, 2024 was $1,937, compared to $1,985 for the three months ended September 30, 2023, a decrease of $48, or 2%. Cost of revenue for the nine months ended September 30, 2024 was $5,851, compared to $5,604 for the nine months ended September 30, 2023, an increase of $247, or 4%.
The decrease in cost of revenue for the three months ended September 30, 2024, was primarily due to lower costs realized from the further integration of our Minnesota manufacturing facility, acquired in the second half of 2023, partially offset by increased manufacturing expenses driven by higher unit sales. The increase in cost of revenue for the nine months ended September 30, 2024, was primarily driven by increased manufacturing expenses resulting from higher unit sales. We anticipate that cost of revenue will continue to increase in future periods in line with the expected growth in unit sales, as described above.
Gross Profit
Gross profit margin for the three months ended September 30, 2024 was 72%, compared to 69% for the three months ended September 30, 2023. Gross profit margin for the nine months ended September 30, 2024 was 70%, compared to 69% for the nine months ended September 30, 2023.
The increase in gross profit margin percentage for both the three and nine months ended September 30, 2024, was primarily due to improvements associated with the integration of our Minnesota manufacturing facility, as well as the further absorption of fixed costs driven by increased unit sales.
General and Administrative
General and administrative expense for the three months ended September 30, 2024 was $6,765, compared to $6,115 for the three months ended September 30, 2023, an increase of $650, or 11%. General and administrative expense for the nine months ended September 30, 2024 was $23,366, compared to $19,977 for the nine months ended September 30, 2023, an increase of $3,389, or 17%.
The increase in general and administrative expenses for the three months ended September 30, 2024, was primarily driven by professional fees for specialized accounting and development work, higher than usual adjustments to the Revo Squared earnout liability in the prior comparative period, and increased amortization expense associated with acquisitions made in the second half of 2023. These increases were partially offset by lower stock-based compensation expense, including the impact of forfeitures related to the departure of our former Chief Financial Officer during the current period. The increase in general and administrative expenses for the nine months