The second-lowest-cost Silver plan is important because its price is used to calculate premium subsidies. For an exchange enrollee with income in the subsidy-eligible range (which has been expanded for 2021 and 2022 under the American Rescue Plan), the subsidy amount is based on the cost of the second-lowest-cost Silver plan in relation to the percent of the enrollee's income that they're expected to pay in after-subsidy premiums. The second-lowest-cost-Silver plan is thus called a benchmark plan because it's the plan that the enrollee will be able to purchase for exactly that percentage of their income; the subsidy amount is benchmarked based on that plan's price. The enrollee can pick a lower-cost plan and pay a smaller amount in premiums, or they can pick a higher-cost plan and pay the difference in additional premiums. The benchmark plan will vary from one part of a state to another, depending on the rating area and plan availability. And the benchmark plan will vary from one year to the next, sometimes being offered by different insurers in different years. This is because the benchmark plan is determined solely based on price: You look at all of the available plans in a given area, arrange them in order by premiums, and the benchmark plan is whatever plan ends up in the second-lowest-cost spot among all the available Silver plans.