The _average_ Y Combinator company is worth ~100M [1]
The _median_ Y Combinator company, however, is worth closer to $0 (the majority of YC companies don't get to a Series A).
This just highlights how counter-intuitive power-law distributions are.
[1] Calculation:
Discard pre YC'17 companies for the purposes of this calculation, as these are still too early stage for meaningful analysis. Brex, Faire and Atrium are the only YC '17 or later on this list.
Numerator: The top 100 companies have a combined valuation of ~$110B, according to this list.
Denominator: There were 1,400 YC companies as of Summer '17 according to https://blog.ycombinator.com/yc-summer-2017-stats/. Removing S17 and W17 gives about 1,100 companies prior to '17
In the most successful class (AirBnB in W09), the majority of companies went to $0. In the most successful recent class (W14), the median startup raised a seed round but nothing else in four years.
Suppose that applying to YC gives you a 1% chance of graduating, this would mean that just applying represents $10k of value!
Of course it doesn't work like this, you need to apply bayesian statistics. Of the great applications almost all get accepted and of the bad applications almost none do.