Cost-to-Charge Ratio

Cost-to-Charge Ratio in Hospital Cost Estimation

A cost-to-charge ratio turns what a US hospital billed into an estimate of what the care cost to produce. Multiplying the total charges on a discharge record by the hospital's ratio gives an estimated cost, which is how cost estimates are drawn from US discharge databases, such as those of the Healthcare Cost and Utilization Project (HCUP), that record charges but not costs. Because charges usually sit well above costs and the gap differs between hospitals and departments, the choice of ratio can move a cost estimate, and any comparison built on it, by a large margin. The ratio also has a second life in Medicare payment, where it decides which cases receive outlier payments.

Where the ratio comes from

The ratio is a by-product of hospital accounting. In their HCUP methods report, Pickens and colleagues trace the national data behind it to the Medicare inpatient prospective payment system of 1983, which needed estimates of the cost of each diagnosis-related group and led to the cost reports that hospitals file with the Centers for Medicare & Medicaid Services (CMS). CMS began releasing these reports publicly around 1995, after which ratios came into wide use for estimating costs for individual hospitals and peer groups, and the Agency for Healthcare Research and Quality (AHRQ) developed its own method in the early 2000s.

Costs in the cost report are grouped by cost centre and include both direct and indirect costs. General service costs such as administration and capital are allocated to the patient care cost centres by accounting formulae, so the numerator carries every assumption of the hospital's cost accounting and cost allocation. Some costs are not allowable, for example payments to physicians employed by the hospital, investment losses and certain advertising, so reported cost may not agree with the hospital's other financial statements. The reporting rules themselves grew out of cost-based reimbursement.

The basic calculation

The ratio divides a hospital's reported cost by the charges billed for the same services in the same period. For hospital $j$ over one cost reporting period, the ratio and the estimated cost of a single stay are as follows.

$$CCR_j = \frac{COST_j}{CHARGE_j}, \qquad \hat{c}_{ij} = CCR_j \times h_{ij}$$

where $CCR_j$ is the cost-to-charge ratio of hospital $j$, $COST_j$ is its total Medicare allowable cost, $CHARGE_j$ is the corresponding total charges, $h_{ij}$ is the total charge recorded for stay $i$ at hospital $j$ and $\hat{c}_{ij}$ is the estimated cost of that stay. Pickens and colleagues describe the ratio as the inverse of the hospital's mark-up, so a ratio of 0.25 means charges run at four times cost.

The same arithmetic can be done within each cost centre, applying a department's own ratio to the charges billed in that department and summing. The charge master page works through a single operation costed both ways. Applying the ratio is a form of top-down costing, since it starts from the hospital's total accounting cost and shares it among patients in proportion to what they were charged.

How the HCUP files are built

AHRQ publishes ready-made ratios to go with the HCUP databases. Its inpatient files hold hospital-specific ratios based on all-payer inpatient cost for nearly every hospital in the State Inpatient Databases and the national samples, and the cost of a stay is estimated by multiplying the total charges variable by the ratio. HCUP total charges exclude professional (physician) fees, so the resulting cost estimates omit physician fees billed separately from the hospital stay.

Pickens and colleagues explain the construction. Cost centres from the Healthcare Cost Report Information System are grouped into service groups, inpatient cost is estimated from each group's share of inpatient charges, and the hospital-level ratio is the sum of inpatient costs divided by the sum of inpatient charges. A hospital-specific ratio is masked when the cost report is missing, incomplete or covers under 180 days, or when the result looks implausible, including a hospital-wide inpatient ratio below 0.05 or above 2. Masked hospitals receive a bed-weighted average for hospitals of the same type in the same state, or the state average. In the 2019 inpatient file, 4,240 hospitals (83.7 per cent) had their own ratio and 824 (16.3 per cent) were given a group average. A separate emergency department ratio covers treat-and-release visits.

Ratios inside Medicare payment

Under 42 CFR 412.84, the cost of an inpatient discharge for outlier purposes is its billed charges for covered services adjusted by the hospital's operating and capital cost-to-charge ratios. Since October 2003 those ratios come from the latest settled or tentatively settled cost report. A statewide average may be used for a new hospital that has not yet filed a cost report, or for one whose ratio is more than 3 standard deviations above the national geometric mean, and outlier payments can later be reconciled using ratios from the cost report for the period of the discharge. How the outlier threshold works is covered under case-based payment.

The 2003 rule shows what goes wrong when charges move faster than costs. CMS found that some hospitals' rate of charge increase greatly exceeded their rate of cost increase, and because ratios lagged behind current charges, the conversion overstated costs and produced excessive outlier payments. Hospitals whose ratios fell below the floor had been given the higher statewide average. In one case the rule describes, charges rose by 60, 35 and 13 per cent in successive years, the hospital's actual operating ratio fell to 0.093 against a floor of 0.194, and it was assigned the statewide average of 0.328. CMS noted that charges are the only data indicating the resource use of an individual case, so identifying true outliers depends on accurate ratios.

Ratios also sit behind the diagnosis-related group relative weight. From fiscal year 2007 Medicare began basing these weights on cost report data rather than charges, phasing the change in over three years, which raised the problem of charge compression, defined in the FY 2009 rule as a higher percentage mark-up on lower cost items and a lower one on higher cost items. Applying one ratio to items of widely varying cost in the same cost centre then undervalues expensive items and overvalues cheap ones. CMS expanded the distinct hospital department ratios from 13 to 15 for FY 2008. Its contractor RTI found charge compression most notably in the medical supplies and equipment ratio, where devices, implantables and prosthetics carried different mark-ups from other supplies.

Worked example of an incremental cost from charges (illustrative)

All figures are illustrative and in USD. An analyst compares medical management (A) with a device-based procedure (B) using charges from one hospital, whose cost report shows costs of USD 300 million against charges of USD 1,000 million. The QALY gain of B over A is taken as 0.10.

1. Hospital-wide ratio. The ratio is 300 / 1,000 = 0.30. Stay A has charges of USD 40,000 and stay B USD 60,000, giving estimated costs of 0.30 × 40,000 = USD 12,000 and 0.30 × 60,000 = USD 18,000.
2. Departmental ratios. Stay A is USD 24,000 of ward charges at a ratio of 0.45 and USD 16,000 of pharmacy at 0.25, so its cost is 10,800 + 4,000 = USD 14,800. Stay B is USD 20,000 of device charges at 0.60, USD 25,000 of theatre at 0.20 and USD 15,000 of ward at 0.45, so its cost is 12,000 + 5,000 + 6,750 = USD 23,750.
3. Incremental cost and ICER. The hospital-wide ratio gives an incremental cost of 18,000 − 12,000 = USD 6,000 and an incremental cost-effectiveness ratio of 6,000 / 0.10 = USD 60,000 per QALY. The departmental ratios give 23,750 − 14,800 = USD 8,950 and 8,950 / 0.10 = USD 89,500 per QALY, about 1.49 times as high.
4. A stale ratio. If the hospital raises all charges by 10 per cent with costs unchanged, stay B is billed USD 66,000. The old ratio gives 0.30 × 66,000 = USD 19,800 against the USD 18,000 estimated before the rise, a 10 per cent overstatement. The correct ratio is 0.30 / 1.10 = 0.273.

The single ratio understates the cost difference mainly because the device in B carries a low mark-up, which outweighs the high mark-up on theatre time in B and the low mark-up on ward care in A. The ICER rises by about half with no change in the care given. A ratio from an earlier year applied to later charges inflates every cost by the factor (1 + charge growth) / (1 + cost growth).

Using converted costs in economic evaluation

Converted charges suit a provider or health system perspective, since they estimate the hospital's cost of producing care. Pickens and colleagues state that charges and costs are distinct from the amounts hospitals receive in payment, so a payer perspective needs paid amounts from claims data instead. Reviewing US administrative data, Riley concluded that cost estimates can vary substantially by measure, whether payments, charges or cost-to-charge ratios, and across data sources. Even the converted figure is an accounting cost, not an opportunity cost.

The ratio works better for averages than for individuals. Using costs from relative value units as the reference, Shwartz and colleagues found that ratio-based costs were not a good basis for the costs of individual patients, but for almost 70 per cent of diagnosis-related groups the average ratio-based cost was within 10 per cent of the reference. An overall hospital ratio was not a good basis for comparing costs between hospitals. Childers and colleagues add that hospital-wide ratios may overestimate costs for surgical patients and may be especially problematic when comparing medical and surgical therapies, the situation in the worked example.

Good practice follows from these findings. The ratio should come from the same hospital and year as the charges, departmental ratios are preferable when the treatments differ in their mix of departments, and professional fees need adding from another source. Plausible alternative ratios belong in a one-way sensitivity analysis when they could change the decision. The method needs a record of list charges, which is why it is used mainly with US hospital data.

Boundaries with nearby concepts

The ratio is easily confused with other ratios built from the same accounts. Under cost reimbursement, Medicare's departmental method shares a department's cost by the ratio of Medicare beneficiaries' charges to total charges, which is algebraically the same as applying the department's cost-to-charge ratio to the beneficiaries' charges, but the purpose there is payment, not estimation. The mark-up is the reciprocal of the ratio. A payment-to-cost ratio compares what a payer paid with estimated cost and measures margin, not resource use. Micro-costing values each resource directly and needs no charges at all.

Common misreadings of the cost-to-charge ratio

Most errors with the ratio come from treating an accounting average as a direct measure of cost or price. Five misreadings follow from that confusion.

1. A lower ratio does not mean a more efficient hospital. It means higher charges relative to cost, which reflects pricing policy as much as productivity.
2. Converted charges are not payments. Charges are recorded before any contractual allowances or discounts, so a converted cost says nothing about what a payer spent.
3. A hospital-wide ratio is an average over departments. It misstates stays that use departments with unusual mark-ups, and charge compression adds error within departments.
4. Ratios age. Applied to later charges, a ratio from an old cost report overstates cost whenever charges grow faster than costs.
5. The numerator is a regulatory cost. Allowable-cost rules and overhead allocation shape it, and non-allowable items are left out.

Sources

• Childers CP, Dworsky JQ, Russell MM, Maggard-Gibbons M. Comparison of cost center-specific vs hospital-wide cost-to-charge ratios for operating room services at various hospital types. JAMA Surgery. 2019;154(6):557-558. https://doi.org/10.1001/jamasurg.2019.0146
• Electronic Code of Federal Regulations. Title 42, section 412.84, Payment for extraordinarily high-cost cases (cost outliers) (as of 1 October 2026). https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-B/part-412/subpart-F/section-412.84
• Electronic Code of Federal Regulations. Title 42, section 413.53, Determination of cost of services to beneficiaries (as of 1 October 2026). https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-B/part-413/subpart-D/section-413.53
• Centers for Medicare & Medicaid Services. Medicare program; change in methodology for determining payment for extraordinarily high-cost cases (cost outliers) under the acute care hospital inpatient and long-term care hospital prospective payment systems. Final rule. Federal Register. 2003;68(110):34494-34515. https://www.govinfo.gov/content/pkg/FR-2003-06-09/pdf/03-14492.pdf
• Centers for Medicare & Medicaid Services. Medicare program; changes to the hospital inpatient prospective payment systems and fiscal year 2009 rates. Final rule. Federal Register. 2008;73(161):48434-49083. https://www.govinfo.gov/content/pkg/FR-2008-08-19/pdf/E8-17914.pdf
• Healthcare Cost and Utilization Project. Cost-to-Charge Ratio for Inpatient Files. Rockville, MD: Agency for Healthcare Research and Quality; 2026. https://hcup-us.ahrq.gov/db/ccr/ip-ccr/ip-ccr.jsp
• Pickens GT, Liang L, Roemer M. HCUP Cost-to-Charge Ratio Methodologies. HCUP Methods Series Report 2021-05. Rockville, MD: Agency for Healthcare Research and Quality; 2021. https://hcup-us.ahrq.gov/reports/methods/MS2021-05-CCR-Methodologies.jsp
• Riley GF. Administrative and claims records as sources of health care cost data. Medical Care. 2009;47(7 Suppl 1):S51-S55. https://doi.org/10.1097/MLR.0b013e31819c95aa
• Shwartz M, Young DW, Siegrist R. The ratio of costs to charges: how good a basis for estimating costs? Inquiry. 1995;32(4):476-481. https://pubmed.ncbi.nlm.nih.gov/8567084/