Table:
|  | Year Ended | Year Ended |
| --- | --- | --- |
|  | December 31, 2019 | December 31, 2018 |
| Expected stock price volatility | 92.34% | 85.26% |
| Risk-free interest rate | 2.09% | 2.73% |
| Expected life term | 6.14 years | 6.02 years |
| Expected dividends | 0% | 0% |
Paragraphs:
The fair value of each option grant was estimated on the date of grant using the Black-Scholes option pricing model using the following weighted average assumptions:
Based on the Black-Scholes option pricing model, the weighted average estimated fair value of employee stock options granted was $4.63 and $2.58 per share during the years ended December 31, 2019 and 2018, respectively.
The expected life was determined using the simplified method outlined in ASC 718, “Compensation - Stock Compensation”. Expected volatility of the stock options was based upon historical data and other relevant factors. We have not provided an estimate for forfeitures because we have had nominal forfeited options and RSUs and believed that all outstanding options and RSUs at December 31, 2019, would vest.
Question:
How was the fair value of each option grant estimated?
Answer: Using the Black-Scholes option pricing model