50m is not the valuation; it's the amount of stock they're selling.

How is that different from the valuation?

If they have 100 shares of stock and are selling 2 at the IPO for 50M then the valuation is much higher than 50M. Just because it is the IPO doesn't mean 100% of the stock is for sell. If they are putting out 20% of their stock then their valuation is 250M.

so what is kayak's actual valuation?

Thanks! I always thought IPO means 100% of the common stock is sold.