american tower corporation and subsidiaries notes to consolidated financial statements 2014 ( continued ) from december 1 through may 31 of each year . during the 2008 , 2007 and 2006 offering periods employees purchased 55764 , 48886 and 53210 shares , respectively , at weighted average prices per share of $ 30.08 , $ 33.93 and $ 24.98 , respectively . the fair value of the espp offerings is estimated on the offering period commencement date using a black-scholes pricing model with the expense recognized over the expected life , which is the six month offering period over which employees accumulate payroll deductions to purchase the company 2019s common stock . the weighted average fair value for the espp shares purchased during 2008 , 2007 and 2006 were $ 7.89 , $ 9.09 and $ 6.79 , respectively . at december 31 , 2008 , 8.8 million shares remain reserved for future issuance under the plan . key assumptions used to apply this pricing model for the years ended december 31 , are as follows: .

Table:
 | 2008 | 2007 | 2006
range of risk free interest rates | 1.99% ( 1.99 % ) 20143.28% ( 20143.28 % ) | 4.98% ( 4.98 % ) 20145.05% ( 20145.05 % ) | 5.01% ( 5.01 % ) 20145.17% ( 20145.17 % )
weighted average risk-free interest rate | 2.58% ( 2.58 % ) | 5.02% ( 5.02 % ) | 5.08% ( 5.08 % )
expected life of the shares | 6 months | 6 months | 6 months
range of expected volatility of underlying stock price | 27.85% ( 27.85 % ) 201428.51% ( 201428.51 % ) | 27.53% ( 27.53 % ) 201428.74% ( 201428.74 % ) | 29.60% ( 29.60 % )
weighted average expected volatility of underlying stock price | 28.51% ( 28.51 % ) | 28.22% ( 28.22 % ) | 29.60% ( 29.60 % )
expected annual dividends | n/a | n/a | n/a
13 .
stockholders 2019 equity warrants 2014in january 2003 , the company issued warrants to purchase approximately 11.4 million shares of its common stock in connection with an offering of 808000 units , each consisting of $ 1000 principal amount at maturity of ati 12.25% ( 12.25 % ) senior subordinated discount notes due 2008 and a warrant to purchase 14.0953 shares of the company 2019s common stock .
these warrants became exercisable on january 29 , 2006 at an exercise price of $ 0.01 per share .
as these warrants expired on august 1 , 2008 , none were outstanding as of december 31 , in august 2005 , the company completed its merger with spectrasite , inc .
and assumed outstanding warrants to purchase shares of spectrasite , inc .
common stock .
as of the merger completion date , each warrant was exercisable for two shares of spectrasite , inc .
common stock at an exercise price of $ 32 per warrant .
upon completion of the merger , each warrant to purchase shares of spectrasite , inc .
common stock automatically converted into a warrant to purchase shares of the company 2019s common stock , such that upon exercise of each warrant , the holder has a right to receive 3.575 shares of the company 2019s common stock in lieu of each share of spectrasite , inc .
common stock that would have been receivable under each assumed warrant prior to the merger .
upon completion of the company 2019s merger with spectrasite , inc. , these warrants were exercisable for approximately 6.8 million shares of common stock .
of these warrants , warrants to purchase approximately 1.8 million and 2.0 million shares of common stock remained outstanding as of december 31 , 2008 and 2007 , respectively .
these warrants will expire on february 10 , 2010 .
stock repurchase programs 2014during the year ended december 31 , 2008 , the company repurchased an aggregate of approximately 18.3 million shares of its common stock for an aggregate of $ 697.1 million , including commissions and fees , pursuant to its publicly announced stock repurchase programs , as described below. .

Question: what was the percentage change in the weighted average risk-free interest rate from 2007 to 2008
Answer: -48.6%
Calculation: subtract(2.58, 5.02), divide(#0, 5.02)