abiomed , inc .
and subsidiaries notes to consolidated financial statements 2014 ( continued ) note 12 .
stock award plans and stock based compensation ( continued ) compensation expense recognized related to the company 2019s espp was approximately $ 0.1 million for each of the years ended march 31 , 2009 , 2008 and 2007 respectively .
the fair value of shares issued under the employee stock purchase plan was estimated on the commencement date of each offering period using the black-scholes option-pricing model with the following assumptions: .

2009
2008
2007
risk-free interest rate
1.01% ( 1.01 % )
4.61% ( 4.61 % )
4.84% ( 4.84 % )
expected life ( years )
0.5
0.5
0.5
expected volatility
67.2% ( 67.2 % )
45.2% ( 45.2 % )
39.8% ( 39.8 % )

note 13 .
capital stock in august 2008 , the company issued 2419932 shares of its common stock at a price of $ 17.3788 in a public offering , which resulted in net proceeds to the company of approximately $ 42.0 million , after deducting offering expenses .
in march 2007 , the company issued 5000000 shares of common stock in a public offering , and in april 2007 , an additional 80068 shares of common stock were issued in connection with the offering upon the partial exercise of the underwriters 2019 over-allotment option .
the company has authorized 1000000 shares of class b preferred stock , $ 0.01 par value , of which the board of directors can set the designation , rights and privileges .
no shares of class b preferred stock have been issued or are outstanding .
note 14 .
income taxes deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to tax benefit carryforwards and to differences between the financial statement amounts of assets and liabilities and their respective tax basis .
deferred tax assets and liabilities are measured using enacted tax rates .
a valuation reserve is established if it is more likely than not that all or a portion of the deferred tax asset will not be realized .
the tax benefit associated with the stock option compensation deductions will be credited to equity when realized .
at march 31 , 2009 , the company had federal and state net operating loss carryforwards , or nols , of approximately $ 145.1 million and $ 97.1 million , respectively , which begin to expire in fiscal 2010 .
additionally , at march 31 , 2009 , the company had federal and state research and development credit carryforwards of approximately $ 8.1 million and $ 4.2 million , respectively , which begin to expire in fiscal 2010 .
the company acquired impella , a german-based company , in may 2005 .
impella had pre-acquisition net operating losses of approximately $ 18.2 million at the time of acquisition ( which is denominated in euros and is subject to foreign exchange remeasurement at each balance sheet date presented ) , and has since incurred net operating losses in each fiscal year since the acquisition .
during fiscal 2008 , the company determined that approximately $ 1.2 million of pre-acquisition operating losses could not be utilized .
the utilization of pre-acquisition net operating losses of impella in future periods is subject to certain statutory approvals and business requirements .
due to uncertainties surrounding the company 2019s ability to generate future taxable income to realize these assets , a full valuation allowance has been established to offset the company 2019s net deferred tax assets and liabilities .
additionally , the future utilization of the company 2019s nol and research and development credit carry forwards to offset future taxable income may be subject to a substantial annual limitation under section 382 of the internal revenue code due to ownership changes that have occurred previously or that could occur in the future .
ownership changes , as defined in section 382 of the internal revenue code , can limit the amount of net operating loss carry forwards and research and development credit carry forwards that a company can use each year to offset future taxable income and taxes payable .
the company believes that all of its federal and state nol 2019s will be available for carryforward to future tax periods , subject to the statutory maximum carryforward limitation of any annual nol .
any future potential limitation to all or a portion of the nol or research and development credit carry forwards , before they can be utilized , would reduce the company 2019s gross deferred tax assets .
the company will monitor subsequent ownership changes , which could impose limitations in the future. .

Question: what is the growth rate in risk-free interest rate from 2007 to 2008?
Answer: -4.8%