Even more striking, for the Chapmans, is this fact: If they made just a few thousand dollars less a year — below $94,200 — their costs would be cut in half, because a family like theirs could qualify for federal subsidies.

The Chapmans acknowledge that they are better off than many people, but they represent a little-understood reality of the Affordable Care Act. While the act clearly benefits those at the low end of the income scale — and rich people can continue to afford even the most generous plans — people like the Chapmans are caught in the uncomfortable middle: not poor enough for help, but not rich enough to be indifferent to cost…

An analysis by The New York Times shows the cost of premiums for people who just miss qualifying for subsidies varies widely across the country and rises rapidly for people in their 50s and 60s. In some places, prices can quickly approach 20 percent of a person’s income.

Experts consider health insurance unaffordable once it exceeds 10 percent of annual income. By that measure, a 50-year-old making $50,000 a year, or just above the qualifying limit for assistance, would find the cheapest available plan to be unaffordable in more than 170 counties around the country, ranging from Anchorage to Jackson, Miss.