Here’s how it works. The exchanges offer individuals a subsidy on a sliding scale, depending on your income, to purchase insurance. If your income is near the poverty line, you get almost a full subsidy. If you make two to three times the federal poverty level—say $25,000 to $35,000 a year for a childless unmarried adult—you get a partial subsidy. And if you make more than four times the federal poverty level—about $46,000 a year—you don’t get any subsidy at all.

But tests on the software that calculates how much your subsidy is worth, if any, only began this week, according to the Journal reporters, even though they were “initially scheduled to begin months ago.” If enrollees’ subsidies are calculated incorrectly, it could mean that some people gain much larger subsidies than they’re eligible for under the law, and others miss out on subsidies they would otherwise obtain. “On the surface, you’d think this is pretty easy for a website to give you a price, but behind the scenes, the number of variables is very high,” says Michael Krigsman, an IT consultant.

In general, when there are problems like this, and the program rolls out anyway, the result is substantial amounts of waste, fraud, and abuse. We already know that the government will be relying on the “honor system” for people to report their incomes, and thereby their eligibility, for exchange subsidies. Combine that with the fact that the exchange software can’t calculate what your subsidy actually is, and the result is that many people will be able to game the system to gain larger subsidies than the law intends.