Enrollments — surprise! — aren’t what they need to be. David Hogberg has the numbers:

Sign-ups of the crucial 18-34-year-old cohort jumped from 25% in early March to 28% at the end of the enrollment period. That’s not a surprise given that young people are likely to be disporportionately represented among people who do things at the last minute. But the fact that over half of that age group chose their plan during the last month should worry ObamaCare supporters. People who are flakey enough to wait until the last minute are probably also flakey when it comes to paying premiums. Thus, that 28 percent number will decline and it will, of course, be no where near the 38 percent the Obama Administration says is needed to keep the risk pools stable. (FYI: The Kaiser Family Foundation says the low number of 18-34-year-olds doesn’t matter much. Seth Chandler says they are wrong.)

While the 18-34-year-old cohort has been dubbed the “young and healthy,” a more accurate moniker might be “young and somewhat healthy.” 68 percent of 18-34-year-olds on the federal exchanges chose a silver plan.

Those Silver plan purchases are the telling detail. If you’re young and healthy, you buy a catastrophic plan if you buy insurance at all. If you’re young and not-so-healthy, you pay up front for more comprehensive coverage. So it would seem that the Young Invincibles are still sitting out, and the Young Hacking Coughs are the ones signing up.

Given the generous subsidies and the higher payouts, it looks like the YHC’s might bust the budget and the exchanges.