How do I find out the value of my vehicle on the date I started using it for business?

[Jimesa]

which year did you begin using it?

[Anita01]

If you started using it in the business right after you bought it, then the value would be the purchase price.  If you started using it after owning it for a  while, the best valuation could be found in the Kelley Blue Book values, which are published online now.