capital growth?

[propertykit]

Hi all,

I bought a house in 2005 to live in and moved out in 2007, it has been renting since then. I just realized that I should get a house valuation done before it became an investment property. I plan to sell the house in 2010, can I do a valuation now in order to help me pay less in capital growth? Can a house valuation be back dated?

Thanks for your help.