While the majority of Medicare recipients could expect to pay just 0.2% more in premiums in 2017, wealthier beneficiaries may face a much sharper increase, the Wall Street Journal writes.

Trustees for the government’s health-care plan said around 30% of the top-earning beneficiaries could be paying up to 22% more next year for Medicare Part B, covering doctor visits and other outpatient care, according to a Boards of Trustees of the Federal Hospital Insurance Trust Fund and the Federal Supplementary Medical Insurance Trust Fund report cited by the Journal.

Such an increase would be a result of the interaction between Medicare and Social Security rules, Tricia Neuman, senior vice president at the Kaiser Family Foundation, tells the publication.

Because of the so-called “hold harmless” provision in the Social Security Act, Medicare’s premium increases can’t be higher than Social Security’s yearly cost-of-living adjustments, the Journal explains. Due to low inflation, that adjustment is expected to be only 0.2% in 2017 — which means Medicare can’t increase its premiums by a bigger amount than the dollar increase in Social Security payments to an estimated 70% of beneficiaries protected by the hold-harmless clause, Neuman tells the Journal.

To offset the increase in costs, Medicare will charge the remaining 30% of beneficiaries if the trustees turn out to be right, the publication writes.

Individuals earning between $85,001 and $107,000 and couples earning between $170,001 and $214,000 could see their monthly premiums go up from $170.50 a person this year to about $204.40 next year, while those earning more than $214,000 and couples earning $428,000 or more could see a jump from $389 to $467.20, according to the Journal. Beneficiaries who fall under the hold-harmless provision, meanwhile, are paying $104.90 a month now, which is equal to their premiums in 2014 because Social Security had no cost-of-living increase this year, the publication writes.

But the Part B premium increase could affect other beneficiaries, such as those who get Medicare but aren’t eligible or have deferred their Social Security benefits, those who will join Medicare in 2017, and those whose premiums are handled by state Medicaid programs, according to the Journal. Last year, 55 million people were covered by Medicare, with 51 million covered by Part B, with those figures projected to rise to 58.7 million and 53.5 million respectively, according to the trustees’ report cited by the publication.

The premium increase may be lower, however, if inflation rises more by October, when the final Social Security cost-of-living adjustments are released, Paul Van de Water, senior fellow at the nonprofit Center on Budget and Policy Priorities tells the Journal. What’s more, Medicare Part B premiums are expected to “reset” for all beneficiaries to $124.40 a month in 2018 because of higher expected cost-of-living increases in Social Security, the publication writes.

Annual Part B deductibles, meanwhile, are projected to rise for all beneficiaries from $166 this year to $204 if the trustees are correct, the Journal writes.

And Medicare Part D monthly premiums, which cover prescription drugs, are projected to rise from $34.10 to $40.59, with higher-earning beneficiaries paying higher premiums, according to the publication.

Meanwhile, Americans aren’t exactly sure what their healthcare costs will be or who’s going to cover them, according to a recent survey cited by MainStreet. According to a report from Alegeus, which assists clients with flexible spending accounts and health reimbursement packages, more than 50% of consumers learn about the cost of a medical service or procedure only when they get the bill, MainStreet writes. And just 35% know the annual cost of their healthcare or what’s covered by their insurance, according to the report. Consumers are also unprepared to foot the bill for serious healthcare costs, according to Alegeus: only 23% save “aggressively” for major issues, the web publication writes.

The average annual cost of healthcare is currently $4,967 but varies from $2,660 for children under 18 to $9,466 for those between 55 and 64, MainStreet writes.

Meanwhile, average annual out-of-pocket costs range from $472 for those under 18 to $1,300 for pre-Medicare adults, according to the publication.