Budget Impact Analysis: What It Is and How It Differs From Cost-Effectiveness Analysis

A cost-effectiveness analysis can show that a new intervention delivers excellent value per unit of health gained and still be unaffordable for the payer being asked to fund it. Budget impact analysis (BIA) is the complementary evaluation that answers the question cost-effectiveness leaves open: not “is this worth its cost,” but “can this specific budget absorb it, and what happens to that budget if we say yes.” Most reimbursement and formulary decisions now require both analyses submitted together, and understanding what each one is actually measuring — and where they can point in different directions — is essential for anyone preparing or reviewing a health-economic submission.

What Question a Budget Impact Analysis Answers

A budget impact analysis projects the net financial impact of adopting a new intervention, technology, or treatment on a specific payer’s budget over a defined time horizon. The unit of analysis is affordability, not value. A BIA does not ask whether an intervention is worth what it costs relative to the health it produces — that is the job of cost-effectiveness analysis, typically expressed as an incremental cost-effectiveness ratio (ICER). A BIA instead asks a narrower, more operational question: given the number of patients likely to receive this intervention, how it will be used relative to what it replaces, and the price at which it will be reimbursed, what is the total additional (or reduced) spending this payer should plan for in year one, year two, and beyond?

The output is a projected budget delta — typically expressed in absolute currency terms and often as a percentage of the relevant total drug or disease-area budget — under a “new intervention” scenario compared with a “current mix of treatments” scenario. A payer can look at a favorable ICER and still reject or delay coverage if the BIA shows the intervention would consume an unsustainable share of the budget in the near term, particularly when the eligible population is large or the time horizon for observing offsetting savings is longer than the budget cycle itself.

How Budget Impact Analysis Differs From Cost-Effectiveness Analysis

The two analyses are frequently confused because they draw on overlapping inputs — clinical trial data, unit costs, resource-use assumptions — but they are built to answer structurally different questions, use different metrics, and are read by different audiences within the same payer organization.

• Question asked. Cost-effectiveness analysis asks whether the intervention is worth its incremental cost per unit of health gained (commonly cost per quality-adjusted life-year). Budget impact analysis asks whether the payer’s budget can absorb the intervention’s adoption, independent of whether it represents good value.
• Metric. CEA typically reports an ICER against a willingness-to-pay threshold. BIA reports a projected total or incremental spend, usually per year, over a multi-year horizon.
• Population framing. CEA is usually calculated per patient or per health outcome and is population-size-agnostic in its core ratio. BIA is explicitly population-scaled — the same per-patient cost profile produces a trivial budget impact for a rare condition and a substantial one for a common condition.
• Time horizon. CEA often models a lifetime horizon to capture downstream health and cost consequences. BIA is deliberately short — ISPOR guidance generally recommends a horizon in the range of one to five years, matched to realistic payer budget-planning cycles, not to the intervention’s full clinical effect.
• Comparator logic. CEA compares the new intervention against a single relevant comparator. BIA compares an entire projected treatment mix “with” the new intervention against the treatment mix “without” it, which is why uptake and displacement assumptions matter so much more in a BIA than in a CEA.

A useful shorthand used across the health-economic evaluation literature, including the CHEERS 2022 reporting standard’s framing of economic evaluation types: cost-effectiveness analysis addresses value-for-money; budget impact analysis addresses affordability. Both are legitimate, necessary questions, and neither substitutes for the other.

The Core Components of a Budget Impact Analysis Model

A properly specified BIA model, consistent with the structure recommended by ISPOR’s Budget Impact Analysis good-practice task force, is built from a small number of interacting components rather than a single formula. Getting any one of these wrong tends to distort the entire projection, because they compound multiplicatively across the model’s time horizon.

Target Population Size

The starting point is an epidemiologically grounded estimate of the eligible population — typically derived from prevalence or incidence data, filtered by the clinical eligibility criteria the intervention’s label or the anticipated coverage policy would actually apply. Overestimating the eligible population is one of the most common sources of an inflated, non-credible budget impact projection; a plausible BIA distinguishes the total diagnosed population from the subset that is actually indicated and likely to be treated.

Uptake and Market-Share Projections

The model then projects, year by year over the time horizon, what share of the eligible population will actually receive the new intervention versus continuing on existing treatments, and how that share is expected to grow (or plateau) as adoption matures. This is usually modeled as two parallel scenarios — the current treatment mix absent the new intervention, and the projected mix once it is available — with the budget impact calculated as the difference between the two scenario totals in each year, not as the standalone cost of the new intervention alone.

Cost Offsets From Displaced Treatments

Because the new intervention typically displaces an existing therapy or reduces downstream resource use (hospitalizations, monitoring, adverse-event management, a less effective comparator’s own drug cost), a defensible BIA nets the new intervention’s direct cost against the costs it avoids. Omitting cost offsets is a common way BIA submissions overstate net budget impact — the gross acquisition cost of a new therapy is rarely the right number to report; the incremental net cost after subtracting displaced spending is.

Time Horizon and Perspective

The model is run over a short, payer-relevant horizon (commonly one to three years, up to five), from the specific payer’s own budgetary perspective — a health plan, a national or provincial health technology assessment (HTA) body, or a hospital formulary — rather than the broader societal perspective a cost-effectiveness analysis might adopt. This is a deliberate methodological choice, not an oversight: a BIA that adopted a societal perspective would answer a different question than the one payers actually need answered when planning next year’s spending.

Why Payers and HTA Bodies Require Both Analyses Together

Reimbursement systems that use formal health technology assessment — including agencies whose processes are documented in guides such as NICE’s technology appraisal process and CDA-AMC’s reimbursement review — routinely require a cost-effectiveness analysis and a budget impact analysis submitted as a paired package, not either one alone. The reasoning is structural: a favorable ICER establishes that an intervention is a good use of health-care resources at the margin, but it says nothing about whether a specific budget, in a specific year, can actually accommodate the aggregate spending that adopting it at scale would require. Conversely, a modest budget impact does not establish that an intervention represents good value; a cheap, low-uptake intervention can still have a poor cost-effectiveness profile.

Payers use the two analyses for genuinely different decisions. The CEA (often synthesized alongside broader evidence through frameworks such as GRADE evidence-to-decision frameworks) informs the coverage decision itself — should this be reimbursed at all, and at what price. The BIA informs implementation and financial planning — how the decision, once made, should be phased, budgeted for, or subjected to a managed-entry agreement or price-volume arrangement if the projected near-term spend is too large to absorb in one step. A large but favorable ICER intervention with a modest eligible population can clear both tests easily; a modestly cost-effective intervention aimed at a very large population can pass the CEA test and still trigger budget-impact-driven negotiation on price, phased rollout, or eligibility restriction. Submitting only one analysis leaves the payer unable to make either kind of decision on its own evidence.

ISPOR’s Good-Practice Recommendations for Budget Impact Analysis

The International Society for Pharmacoeconomics and Outcomes Research (ISPOR) publishes the field’s principal methodological reference for BIA, Principles of Good Practice for Budget Impact Analysis II, developed by its Budget Impact Analysis good-practice task force and published in Value in Health. The task force’s recommendations, still the standard cited by HTA bodies and payers when specifying submission requirements, converge on the components above: model the current and new treatment-mix scenarios explicitly rather than presenting the new intervention’s cost in isolation; ground the eligible population in real epidemiological data rather than total prevalence; use a short, decision-relevant time horizon; adopt the specific payer’s own budgetary perspective; and report results transparently enough — including the underlying uptake and cost-offset assumptions — that a reviewer can test the model’s sensitivity to each one, typically alongside a one-way sensitivity analysis of the parameters the projection is most sensitive to.

Common Pitfalls in Budget Impact Models

A handful of errors recur across BIA submissions and are worth checking for specifically when reviewing or building one. Modeling the new intervention’s gross cost without netting out displaced-treatment offsets systematically overstates net impact. Using a population estimate drawn from total disease prevalence rather than the clinically eligible, treatment-eligible subset produces an implausibly large denominator. Choosing a time horizon that is either too short to reflect realistic uptake ramp-up or long enough to blur into cost-effectiveness territory undermines the analysis’s distinct purpose. And presenting a single point estimate without any sensitivity analysis on uptake, price, or population size leaves a reviewer unable to judge how much the projection depends on the analyst’s own assumptions — a defensible BIA reports a range, not just a headline number.

Frequently Asked Questions

Is a budget impact analysis the same thing as a cost-effectiveness analysis?

No. They are complementary but distinct evaluations. Cost-effectiveness analysis measures value — whether the health gained justifies the cost, usually as an ICER. Budget impact analysis measures affordability — the projected change in a specific payer’s total spending over a defined horizon. An intervention can be highly cost-effective and still have a large budget impact if the eligible population is large, and can have a small budget impact while being poor value if uptake or the eligible population is small.

What time horizon does a budget impact analysis typically use?

ISPOR’s good-practice guidance generally recommends a horizon of roughly one to five years, matched to the payer’s actual budget-planning cycle, in contrast to the lifetime or multi-decade horizons common in cost-effectiveness models. The shorter horizon reflects the BIA’s purpose — near-term financial planning — rather than the full downstream clinical and cost consequences a CEA is designed to capture.

Why does the eligible population size matter so much in a BIA but less in a CEA?

A cost-effectiveness ratio is typically calculated per patient or per health outcome and does not scale with how many patients receive the intervention. A budget impact analysis is explicitly population-scaled: it multiplies a per-patient cost difference by the projected number of patients treated each year, so the same clinical and cost profile can produce a negligible budget impact for a rare condition and a substantial one for a common condition.

What counts as a cost offset in a budget impact model?

A cost offset is spending the payer avoids because the new intervention displaces or reduces the need for something else — commonly the acquisition cost of the therapy it replaces, but also downstream resource use such as hospitalizations, adverse-event management, or monitoring visits the comparator required. A budget impact analysis that reports only the new intervention’s acquisition cost without netting out these offsets overstates the true net impact on the payer’s budget.

Do all HTA bodies require both a CEA and a BIA?

Most formal HTA processes that assess new health technologies for reimbursement request both, though the specific submission templates and required detail vary by jurisdiction. The pattern holds across major HTA systems: the cost-effectiveness case establishes whether the intervention is good value, and the budget impact case establishes whether and how quickly the payer’s budget can absorb it, and the two are reviewed together rather than as substitutes for each other.