Basic net loss per share is determined by dividing net loss by the weighted average shares of common stock outstanding during the period, without consideration of potentially dilutive securities, except for those shares that are issuable for little or no cash consideration. Diluted net loss per share is determined by dividing net loss by diluted weighted average shares outstanding. Diluted weighted average shares reflects the dilutive effect, if any, of potentially dilutive common shares, such as stock options and warrants calculated using the treasury stock method. In periods with reported net operating losses, all common stock options and warrants are generally deemed anti-dilutive such that basic net loss per share and diluted net loss per share are equal.

The following potentially dilutive securities were excluded from the computation of earnings per share as of June 30, 2021 and 2020 because their effects would be anti-dilutive:

	June 30,
	2021		2020
Stock options		1,091,888		1,640
Common stock warrants - equity		3,773,266		4,051,499
Common stock reserved for conversion of preferred shares		1,170,700		2,595,087
Assumed conversion of convertible notes		154,222		146,288
Total		6,190,076		6,794,514

At June 30, 2021, the Company had 156,000 pre-funded warrants outstanding. The following table provides a reconciliation of the weighted average shares outstanding calculation for the three and six months ended June 30, 2021 and 2020:

	Three months ended June 30,				Six months ended June 30,
	2021		2020		2021		2020
Weighted average shares issued		6,511,194		2,038,297		6,319,622		1,054,549
Weighted average pre-funded warrants		170,175		234,890		270,033		117,445
Weighted average shares outstanding		6,681,369		2,273,187		6,589,655		1,171,994