CFD Valuation: CFDs are valued at the same price of the underlying asset they are derived from. The valuation is highly accurate when compared with other derivatives such as futures or options. The CFD will almost follow the value of the underlying asset perfectly.
The underlying asset of a CFD can be a share, index, currency, commodity or other. There is no separate formula for the valuation of CFDs, the valuation techniques all come from analyzing the underlying asset its self.
So if a stock is trading at $20 per share, the CFD will also be trading at the same level. The stock ticks also happen in real time so its just like trading the stock (or whatever the underlying asset is). Even large purchases are represented in the price as the broker will usually open a position on the relative market impacting the price and thus rolling back to the CFD price.