Mark Suster Partner Upfront Ventures and former entrepreneur
“Valuation = whatever an investor is willing to pay. Investors want to own 25-33% so it can be determined by how much you raise.  early investors know how much they want to invest and what the norms are by stages. There are huge variances (and prices go up and down dependent on market conditions), but general guidelines on valuation:
angel: sub $1m
seed $1-$2.5m pre [pre-money valuation]
A round: $2-5m pre. Up to $7-8m for super experienced entrepreneurs
B round $7-12m pre. Outliers can be $20m pre. EXTREME outliers (see: FourSquare) can fetch crazy prices.
C round: 100% dependent on company performance.”
Mark Suster comments from Want to Know How VC’s Calculate Valuation Differently from Founders?, July 22, 2010; http://www.bothsidesofthetable.com/2010/07/22/want-to-know-how-vcs-calculate-valuation-differently-from-founders/