is recognized, a simultaneous adjustment for returns is estimated, reducing revenue. Estimated return credits are presented as a reduction to gross sales with the corresponding reserve presented as customer contract liabilities.
Variable consideration related to unused shock credits is calculated using the expected value method, which estimates the amount that is expected to be earned. Estimated amounts are included in the transaction price to the extent it is probable that a significant reversal of cumulative revenue recognized will not occur. Estimates of variable consideration are based upon historical experience and known trends. These estimated credits are non-refundable and may only be used towards the purchase of future trode refurbishments. This practice encourages refurbishment purchase prior to complete utilization of the previous trode, so the customer will always have a trode at hand with ample capacity to perform treatments.
The number of trodes returned by year is tracked against the number of trodes sold in that same year, creating a current experience rate. It is assumed that the ultimate return rate for the trodes is 98%. For annual calculations, it is assumed that the expected returns in the current year for each layer increase to the experience rate of the year immediately preceding it. Once the 98% is reached the layer is removed from the calculation. The annual incremental change in expected returns is multiplied by an average return credit amount, generating the current liability due to customers.
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.
On September 30, 2022, the estimated value of our Therapeutics customer contract liability was $418. If the expected return rate was increased by 2%, the effect on current year reduction in sales and increase in customer liability would have been approximately $26.
Results of Consolidated Operations
Revenue
Revenue for the three months ended September 30, 2022 was $4,776, compared to $23 for the three months ended September 30, 2021, an increase of $4,753 or 20,665%. The increase was primarily due to the inclusion of our PulseVet platform and Assisi products which had revenues of $4,682 consisting of consumables, instruments, trodes, and warranty services sold worldwide. Revenues from sales of cartridges from our TRUFORMA platform were $94 compared to $23, an increase of $71 or 309%.
Revenue for the nine months ended September 30, 2022 was $12,773, compared to $52 for the nine months ended September 30, 2021, an increase of $12,721 or 24,463%. The increase was primarily due to the inclusion of our PulseVet platform and Assisi products which had revenues of $12,531 consisting of consumables, instruments, trodes, and warranty services sold worldwide. Revenues from sales of cartridges from our TRUFORMA platform were $242 compared to $52, an increase of $190 or 365%.
We launched our TRUFORMA platform in March 2021, acquired PulseVet in October 2021, and acquired Assisi in July 2022. In general, we expect revenue to increase in subsequent periods as we increase our sales and marketing of the PulseVet platform and Assisi products and as additional assays are added to our TRUFORMA platform.
Cost of Revenue
Cost of revenue for the three months ended September 30, 2022 was $1,215, compared to $18 for the three months ended September 30, 2021, an increase of $1,197 or 6,650%. Cost of revenue primarily resulted from costs associated with sales of our PulseVet platform and Assisi products which totaled $1,171, as well as $44 from costs associated with sales of our TRUFORMA platform.
Cost of revenue for the nine months ended September 30, 2022 was $3,415, compared to $59 for the nine months ended September 30, 2021, an increase of $3,356 or 5,688%. Cost of revenue primarily resulted from costs associated with sales of our PulseVet platform and Assisi products which totaled $3,266, as well as $149 from costs associated with sales of our TRUFORMA platform.
We anticipate that costs of revenue will increase in 2022 in accordance with the increased revenue as described above.
Gross Profit Margin
Gross profit margin for the three months ended September 30, 2022 was $3,561 or 75%, compared to $5 for the three months ended September 30, 2021, an increase of $3,556.