The Affordable Care Act's tax penalty for people who opt out of health insurance is one of the most loathed parts of the law, so it is no surprise that Republicans are keen to abolish it. But the penalty, also called the individual mandate, plays a vital function: nudging healthy people into the insurance markets, where their premiums help pay for the cost of care for the sick. Republican lawmakers think they have a better alternative.The GOP approach is called a "continuous coverage" penalty. It increases the cost of the premiums for anyone buying an individual insurance policy if they have gone 63 or more consecutive days without health insurance in the previous 12 months. Their monthly premiums would rise by 30 percent, and that surcharge would last for a year. While Obamacare assesses a fine for each year people don't buy insurance, the GOP plan would punish those who decide to purchase health insurance for the first time ever, or after a lapse.Much is at stake. If the GOP approach fails to prod enough healthy people into buying insurance, rates for everyone else in the insurance pool will rise — destabilizing promises by President Donald Trump and GOP leaders to make their Obamacare replacement more affordable.The nonpartisan Congressional Budget Office projects that millions fewer people will buy insurance if the individual mandate is repealed and replaced with a continuous coverage surcharge.Why do people allow their insurance to lapse?Some consumers, like Sheila Swartz, who lives outside Nashville, Tenn., and works as a house cleaner, simply can't afford the premiums. She and her husband, Don, who has a heart condition, dropped their policy in December after learning monthly premiums were going to increase by about $140 to $530."You can't get blood out of a turnip," Swartz said. "If you can't afford that premium, you can't afford that premium."Others stop paying premiums when they lose a job or are hit with unexpected costs in other areas, such as major repairs to a car or home.If you find yourself having to choose between paying rent versus health insurance, "you are probably not going to choose health insurance," said Bruce Jugan, a health insurance broker in Montebello, Calif.Some people try to game the system, taking the calculated risk of going without insurance until they get sick or know they need expensive medical care — such as to cover the costs pregnancy and childbirth, or an elective surgery.Both the Affordable Care Act and the GOP proposal include a deterrent by restricting people from enrolling anytime they want. Instead, applicants must wait for annual enrollment periods, usually in the final weeks of the year, meaning that some people might have to wait months before getting coverage. (Applicants still can get insurance during special enrollment periods if they lose a job, get divorced or have another specified major life change.)How tough is the GOP penalty compared with the individual mandate?Under the ACA, the average individual mandate penalty in 2015 was $442, according to the Internal Revenue Service. The GOP penalty would vary, based on cost of premiums, but generally would be more expensive than paying the mandate's penalty. A 40-year-old with annual premiums of $4,328 would pay an extra $1,298 because of the GOP surcharge."It's got teeth," said Cheryl Damberg, a RAND Corp. economist. "In some ways, it's a more punishing penalty, and it's going to hit people who are least capable of financially affording it."Seth Chandler, a law professor at the University of Houston Law Center, who has been critical of the Affordable Care Act's insurance markets, said he is skeptical the GOP surcharge is high enough to make people enroll."I am concerned that the Republicans are succumbing to the same softness of heart as the Democrats succumbed too when they set the individual mandate [penalty]," he said. "If you start to see insurance companies object or drop out of the markets, that's a sign this thing is miscalculated."Two conservative economists at the American Enterprise Institute, Joseph Antos andJames Capretta, see the penalty as "far too small" to be effective. "Healthy consumers are likely to take their chances," they wrote in this month's issue of Health Affairs Blog. "With the repeal of the individual mandate, and the retention of the ACA's insurance rules, the overall effect would be significant market turbulence, starting immediately in 2017."The CBO has predicted there would be a brief increase in the number of people holding insurance in 2018, under the GOP plan, as roughly 1 million people buy coverage to avoid the surcharge. In most years afterward, however, about 2 million fewer people would be expected to buy policies, either because of the surcharge or because of the requirement that they provide documentation proving they've been insured. The CBO predicted that healthy people in particular would be more likely to avoid buying policies.The plan has some parallels to Medicare's late-enrollment penalty, which is applied to premiums for people who don't sign up when they turn 65. But Christopher Koller, a former Rhode Island health insurance commissioner, doubts the GOP penalty would be as effective."Medicare is an entitlement with the force of government behind it," said Koller, now president of the Milbank Memorial Fund, a foundation in New York that does health policy analysis. "You get lots of notices about what your obligations are as you approach that age."What about people who can't afford premiums?The GOP surcharge would contain no hardship exemptions, unlike the individual mandate, which allows people to escape paying a penalty if premiums would eat up too much of their income (8.16 percent in 2017).In 2015, 5.6 million people paid the individual mandate penalty, but another 11 million claimed a hardship exemption, according to the IRS.Lower-income people are going to have even more trouble buying — and keeping — coverage under the GOP plan, health care analysts said. The ACA's subsidies to help pay monthly premiums are based on income, and millions of people on the poorer end of the spectrum do not have to pay anything toward their premiums if they choose the cheapest plan. The GOP plan, on the other hand, would offer a flat tax credit that adjusts only for age. The penalties would make some people even more reluctant to buy insurance — especially if they are relatively healthy."I think we would just end up with a lot more uninsured people, and they would clearly be the type of people who are less able to navigate [the insurance system] and less able to afford insurance," said Geoffrey Joyce, director of health policy for the University of Southern California Schaeffer Center for Health Policy & Economics.Republican lawmakers have said their plan rightly places the responsibility on individuals. That's a view shared by some health insurance brokers, including Helena Ruffin, president of the Ruffin Group Insurance Services in Playa Vista, Calif. A continuous coverage requirement would "limit those people who are not playing by the rules," she said."I am favor of the penalties," said Ruffin. "Whether or not people are going to pay attention is another story." Kaiser Health News, a nonprofit health newsroom whose stories appear in news outlets nationwide, is an editorially independent part of the Kaiser Family Foundation. Jordan Rau and Anna Gorman are senior correspondent for KHN. Copyright 2017 Kaiser Health News. To see more, visit Kaiser Health News.