What it means
Medicare has two main funding streams. Hospital Insurance, or Part A, is financed largely by payroll taxes held in a trust fund.
Supplementary Medical Insurance covers Part B and Part D and has its own trust fund, supported by member premiums and by contributions from general government revenue. The word supplementary can mislead people.
It does not mean an optional extra policy bought in addition to Medicare, such as Medigap. It simply signals that this part was added to the original hospital cover to provide medical services such as doctor visits.
Because a large share of the funding comes from general revenue, the cost to the government grows with the cost of care. That makes the SMI fund a focus of budget debates and long-term projections.
Unlike the hospital fund, it is designed to be balanced each year, since the government sets premiums and contributions to cover expected costs. For individuals, the practical effect is that Part B and Part D premiums are set to cover only a share of the real cost of the care.
The government's contribution is what keeps the premiums affordable. Higher earners pay a larger share through income-related charges.
Finance professionals meet the concept when valuing retiree health obligations and when reading government fiscal reports. Understanding that SMI is partly premium-funded and partly tax-funded helps explain why policy changes to Medicare can affect both household budgets and national deficits.
Terminology can vary by source, and some documents use SMI to refer to Part B alone. Always check the definition in the document you are reading before comparing numbers.
In practice
Real-world examples.
Example
A policy analyst writing about government finances explains that SMI spending is financed partly by premiums and partly by general revenue. She shows that if costs rise by 5%, premiums and tax contributions must both rise. Her note helps readers see why the programme is a budget issue. She includes a simple chart showing how the premium share and the tax share change together.
Example
A retiree wonders why his Part B premium goes up every year. His adviser explains that the premium is set to cover a share of the expected cost of SMI, so rising medical costs push it higher. They plan for annual increases in his retirement budget. He also keeps a small reserve in case the income-related charge applies to him in a future year.
Example
A pension actuary values a company's retiree health promise and notes that the obligations depend on Part B and Part D costs. She uses projected premium growth in her model. The result affects the liability shown on the balance sheet. She documents her premium growth assumption so the auditors can review it.
Case study
Seen in the real world.
Ironwood Capital is an illustrative, fictional asset manager whose analyst, Priya, was preparing a briefing for clients on long-term government spending. She wanted to explain why health costs for older people were a concern.
She explained that SMI is funded by premiums and general revenue, and that when costs rise, the government must find extra revenue each year. Using an illustrative assumption that annual SMI spending of $400,000,000,000 grew by 6%, the increase would be 400,000,000,000 x 0.06 = $24,000,000,000.
Clients understood that the pressure falls on the budget as well as on retirees. The illustrative lesson is that knowing how a programme is funded helps you see who bears the cost of changes. She also reminded them that individual retirees feel the same pressure through higher premiums, so the national picture and the household picture are linked.
Watch out
Common mistakes.
- Thinking that supplementary means an optional private policy, when it is a core part of Medicare that covers Parts B and D.
- Assuming member premiums cover the whole cost of care, when general government revenue pays a large share.
- Treating SMI as the same as Medigap, when Medigap is private insurance that fills gaps in original Medicare.
Questions
People also ask.
Which parts of Medicare does SMI cover?
It covers Part B, for doctors and outpatient care, and Part D, for prescription drugs. Because Part B covers services given outside hospitals, it is the part most people use routinely, such as visits to a doctor or specialist.
How is SMI funded?
It is funded partly by member premiums and mainly by contributions from general government revenue. The prescription drug part is financed in a related way, with premiums, government contributions and payments from the plans involved.
Is SMI the same as Part A?
No, Part A is hospital insurance funded mainly by payroll taxes, while SMI covers other medical services. Part A has its own separate trust fund, so the two sets of accounts are reported and projected separately in government documents.
From the founder's library
Take it further with the book.
Build your financial confidence beyond this definition. Shihan's full-length guide, Accounting Fundamentals, takes the same plain-English approach and turns it into a complete, practical playbook for non-finance managers, business owners and students - with chapter-end quiz answers and presentation slides included.
25% off with code MMHQ25, applied at checkout. Priced in USD - checkout may show the equivalent in your local currency.
View the book and save 25%Related