That investment amount seemed low, as it suggested you weren't exercising your pro rata rights. If the initial $400k bought 10% of the company, USV would need

That investment amount seemed low, as it suggested you weren't exercising your pro rata rights. If the initial $400k bought 10% of the company, USV would need to buy 10% of each subsequent round to maintain their ownership, which would be ~$12.5M. That's ignoring varying definitions of pro rata rights, other dilution but probably a good lower bound. If the initial $400k bought 20% (more likely for Tumblr in 2007), USV invested ~$25M to keep their ownership stake. Fred seems like the kind of guy who always does his pro rata, so I'd imagine those numbers are closer to reality.