10. INCOME TAXES

As of March 31, 2023 and December 31, 2022, the Company maintained a valuation allowance of $86,120 and $84,952, respectively. The valuation allowance was recorded due to the fact that the Company has incurred operating losses to date.

Realization of deferred tax assets is dependent upon future earnings, if any, the timing and amount of which are uncertain. Accordingly, the net deferred tax assets have been fully offset by a valuation allowance. The valuation allowance increased by approximately $1,200 during the three months ended March 31, 2023 and decreased by approximately $17,100 during the three months ended March 31, 2022.

The effective tax rate differs from the statutory tax rate of 21% due to the effect of stock compensation, accrued dividends on convertible preferred stock, executive compensation, other permanent differences and state taxes.

Total U.S. federal and state operating loss carryforwards as of March 31, 2023 and December 31, 2022 were approximately $787,000 and $786,600, respectively. U.S. federal net operating loss carryforwards begin to expire in 2033, and state operating loss carryforwards begin to expire in 2027. U.S. federal net operating losses of approximately $417,300 carry forward indefinitely.

As of March 31, 2023, the Company’s federal research and development credit carryforwards for income tax purposes were approximately $1,200. If not used, the current carryforwards will expire beginning in 2034.

Due to the net operating loss carryovers, the statute of limitations remains open for federal and state returns.

The Company has completed a review to determine whether the future utilization of net operating loss and credit carryforwards will be restricted due to ownership changes that have occurred. Due to the Engine Acquisition, the Company experienced an ownership change on February 17, 2022. Thus, the Company's net operating loss carryforwards are subject to an annual limitation of approximately $8,200 per year. The Company had a net unrealized built-in gain corporation on the ownership change date and had a net unrealized built-in gain of approximately $330,700 at the change date. As a result, under the section 338 Approach of Notice 2003-65, the Company's annual limitation is expected to be increased in the first five years post-change by approximately $121,400. Based on the February 17, 2022 limitation, all of the total net operating loss carryforwards are expected to become utilizable by the tax year ending December 31, 2043.
 

The Company also acquired federal net operating losses in the Engine Acquisition. It was determined that the Engine net operating losses acquired are also subject to a Section 382 annual limitation of approximately $3,800 due to Engine's ownership changes in both 2018 and 2022. Engine is a net unrealized built-in gains ("NUBIG") corporation and had a NUBIG of approximately $265,200 at the change date. As a result, the Engine annual limitation is expected to be increased in the first five years post-change by an aggregate of approximately $87,800. As of the 2022 ownership change, approximately $3,100 of the net operating losses that were restricted by the 2018 ownership change had freed up and become available for use, and approximately $6,000 remained restricted. A further approximately $55,000 in net operating losses had been generated between the date immediately following the 2018 ownership change and the 2022 ownership change. Of the approximately $58,100 in net operating losses that were now solely limited by the section 382 limitation resulting from the 2022 ownership change, all of the total net operating loss carryforwards are expected to become utilizable by the tax year ending December 31, 2025. The remaining approximately $6,000 in net operating loss carryforwards still subject to the section 382 limitation resulting from the 2018 ownership change are expected to free up and become available for use by the tax year ended December 31, 2049. None of the pre-change net operating losses subject to the July 31, 2018 and February 17, 2022 limitation are expected to expire unutilized as a result of both ownership changes.