There is a model used to value warrants which is called the black scholes model. This model traditionally has 6 inputs: stock price, strike price, expected term, volatility, dividends, and risk free rate. I used the number 1.37 as an example how I like to find the risk free rate when I use the black scholes model. The risk free rate is the rate of return you could expect if you invested your money in an investment with no risk i.e. T-Bills.