They don't cover the exact same date range (20y has 10 more years of 20y returns than the 30y), plus it's a median so it could be randomness that skewed it towa

They don't cover the exact same date range (20y has 10 more years of 20y returns than the 30y), plus it's a median so it could be randomness that skewed it towards a higher return vs. the 30y. (The 10.21% return happened 1 year before the first 30y return is recorded.) Interesting that if you take the mean you get: 10y, 20y, 30y :: 8.87%, 9.67%, 10.23% Increasing mean returns as you increase holding period, and the mean 30y is almost exactly the median 20y.