The Kaiser Family Foundation took a crack at solving one big mystery of the House health care bill: how many people with pre-existing conditions might be vulnerable to higher premiums in states that get waivers from Affordable Care Act rules. The answer, in a report out this morning: 6.3 million people.

Why it matters: If that many people could be hit with higher rates, the $8 billion fund to help covet their costs could be stretched pretty thin.

Here's how they figured it out:

• Under the amendment by Rep. Tom MacArthur, states would be able to get waivers from the rules that prevent insurers from charging higher rates to sick people.
• But people with pre-existing conditions would only be vulnerable if they had a lapse in coverage of 63 days or longer.
• So Kaiser looked at all of the people who had a long break in coverage in 2015, using data from the National Health Interview Survey.
• It found 27.4 million people with a lapse in coverage.
• Of those. 6.3 million — 23 percent — had a pre-existing condition.

Yes, but: That's probably a ceiling for how many people could be affected. Not every state will apply for a waiver — in fact, there's no sure way to estimate how many will. And as Kaiser noted, some people will have a stronger incentive to avoid a break in coverage, if they can.