| Income tax expense differs from statutory amounts |
Income tax expense differs from the statutory amounts as follows: | | | 2017 | | 2016 | | | | | | | | | | | | Income taxes at U.S. statutory rate | | $ | (9,289,000) | | $ | (7,437,000) | | | Current year reserve | | | (25,175,000) | | | 7,423,000 | | | Expenses not deductible | | | 46,000 | | | 14,000 | | | Rate change | | | 34,418,000 | | | - | | | | | | | | | | | | Total tax expense | | $ | - | | $ | - | |
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| Temporary differences that give rise to deferred tax assets (liabilities) |
The temporary differences that give rise to deferred tax assets and liabilities were as follows: | | | December 31, | | | | | 2017 | | 2016 | | | Deferred tax assets (liabilities): | | | | | | | | | Net operating loss carryforwards | | $ | 50,029,000 | | $ | 73,864,000 | | | General business credit carryforwards | | | 3,227,000 | | | 2,557,000 | | | State credits | | | 3,089,000 | | | 3,089,000 | | | Property, equipment and goodwill | | | (28,000) | | | (23,000) | | | Stock options | | | 5,122,000 | | | 6,450,000 | | | Derivatives | | | (57,000) | | | (92,000) | | | Deferred revenue | | | 778,000 | | | 1,464,000 | | | Intangible assets | | | 379,000 | | | 228,000 | | | Accrued interest | | | 156,000 | | | 253,000 | | | Other | | | 143,000 | | | 231,000 | | | Gross deferred tax assets | | | 62,838,000 | | | 88,021,000 | | | Valuation allowance | | | (62,838,000) | | | (88,021,000) | | | Net deferred taxes | | $ | - | | $ | - | |
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| Net operating loss carryforwards and general business credits expiration dates |
These carryforwards expire as follows: | | | Net operating loss carryforwards | | General business credit
carryforwards | | | 2018 | | $ | 3,324,000 | | $ | 112,000 | | | 2019 | | | 3,306,000 | | | 95,000 | | | 2020 | | | 5,125,000 | | | 226,000 | | | 2021 | | | 5,378,000 | | | 56,000 | | | Thereafter | | | 221,102,000 | | | 2,165,000 | | | | | $ | 238,235,000 | | $ | 2,654,000 | |
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