Medicaid supplemental payment programs are one of the more confusing corners of public-sector healthcare finance. They sound like a discount or a rebate, but they’re actually a parallel payment mechanism — separate from the base Medicaid claim — designed to close the gap between what Medicaid pays and what care actually costs.
For ambulance services, the relevant supplemental payment program is GEMT (Ground Emergency Medical Transportation). Here is how the mechanism works.
The problem the program solves
Medicaid pays ambulance providers a base rate per emergency transport plus a per-mile rate. For most services — especially rural and volunteer departments — those rates do not cover the actual cost of putting an ambulance on the road. The fixed costs of staffing, training, vehicles, and equipment do not scale down to match a low transport volume.
The federal government allows states to close that gap using federal Medicaid matching funds, on the condition that the non-federal share of the supplemental payment comes from a qualifying source — typically a unit of local government.
How the money flows
The flow is counterintuitive the first time you see it:
- The public ambulance service or its parent jurisdiction transfers funds to the state. This is the intergovernmental transfer (IGT) — the non-federal share of the supplemental payment.
- The state draws federal Medicaid matching funds on top of the IGT. In Iowa, the federal match rate (FMAP) typically covers a majority of the total payment.
- The state pays the combined amount back to the ambulance service as a Medicaid supplemental payment.
The net effect: the service ends up with substantially more revenue than it transferred in, because the federal match is added in the middle.
Why the IGT exists
States cannot use their own general fund or any federally-derived funds as the non-federal share. The IGT is the legally-prescribed mechanism for getting non-federal dollars into the state Medicaid account so the federal match can attach.
This is also why only publicly owned or operated services qualify for GEMT. Private companies cannot make an IGT — they’re not units of government.
The cost report is the gatekeeper
The supplemental payment amount is not invented. It is calculated from the annual cost report, which establishes:
- The total cost of providing emergency ground transports for the year
- An average cost per transport
- The gap between that cost and what Medicaid already paid (base + mileage)
That per-transport gap, multiplied by the number of GEMT-eligible Medicaid transports, becomes the supplemental payment.
How this differs from a rate increase
Supplemental payments are paid separately from Medicaid claims. They do not change the base rate. They are calculated and paid annually, prospectively, based on prior-year cost data. Each year, eligibility, the cost report, and the IGT all have to be renewed.
In other words: there is no point at which a service “is on” the program and the payments just keep flowing. The work is annual.
If you don’t file the cost report, the supplemental payments stop. Even if you filed last year. Even if your eligibility hasn’t changed.
What this looks like in practice
For a typical Iowa publicly operated ambulance service running a few hundred GEMT-eligible transports per year, the annual supplemental payment can be a meaningful share of the service’s total Medicaid revenue. The exact figure depends on cost per transport, transport volume, and prior-year reimbursement — and changes each year.
The discipline of doing the cost report well is what determines how much of the available payment your service actually receives.