Medical Event Cost Estimator: What Will This Health Event Actually Cost Me?

Why this tool exists

US health insurance bills people in a multi-stage waterfall — deductible first, then coinsurance, then the out-of-pocket maximum kicks in. Most people understand each part separately but can't tell you what a $20,000 outpatient surgery would actually cost them until the bill arrives.

That uncertainty drives two real problems: under-sized emergency funds (people budget for $2K shocks when the realistic worst case is $9K+), and bad open-enrollment decisions (people pick HDHPs without checking what their max exposure actually is). This tool answers the specific question "given my plan, what would event X cost me?" — with the formula visible and your inputs never leaving the browser.

How the math works

The standard US health insurance waterfall (ACA-compliant plans, HDHP-style framing):

1. You pay 100% of the allowed amount (insurance-negotiated rate) until your annual deductible is met.
2. Above the deductible, you pay the coinsurance share (e.g. 20%); insurance covers the rest.
3. Total annual patient out-of-pocket capped by the out-of-pocket maximum — ACA's 2025 individual ceiling is $9,200 per HHS Notice of Benefit and Payment Parameters.

The preset event amounts come from Kaiser Family Foundation (KFF) and the Peterson-KFF Health System Tracker on typical allowed amounts in 2022-2024 data, plus the HCUP National Inpatient Sample for hospital stays and CMS hospital outpatient payment data. These are rough national averages — actual rates vary materially by region, facility, in-network vs out-of-network status, and the clinical specifics of your visit.

What this tool doesn't model (yet): PPO-style flat copays for office visits and ER (some plans), separate out-of-network OOP maximums, premium share, surprise billing for out-of-network providers at in-network facilities (mostly addressed by the No Surprises Act 2022 but with exceptions), and the HSA pre-tax effect on dollar value (use the HSA Optimizer for that).

Math runs locally. Inputs never leave your browser. Source on github.

When this estimate will be wrong

• Out-of-network care. Going out-of-network typically triggers a separate (higher) deductible and OOP max, and the provider isn't obligated to accept the insurance-negotiated rate. The No Surprises Act (2022) addresses some of this but not all — anesthesia and ground ambulance are common exceptions.
• Plans with flat copays. Many PPO plans use copays (e.g. $40 office visit, $250 ER) instead of coinsurance for certain services. Copays typically count toward the OOP max but not the deductible. This MVP simplifies that to coinsurance-only.
• Pharmacy benefits separately tiered. Most plans treat prescriptions under a separate formulary with its own copay/coinsurance structure. Chronic-Dx events estimated here exclude prescription costs.
• Allowed amount varies by 3× across markets. A hip replacement allowed amount is ~$15K in low-cost markets and ~$45K in high-cost metros (per the RAND Hospital Price Transparency Study). Our presets are mid-range estimates — call your provider's billing office for a specific quote if a procedure is scheduled.

What to actually do with this number

1. Use your OOP max as the worst-case medical line item in your emergency fund target. If your OOP max is $9,200, a 6-month emergency fund should fully cover one max-out year plus living expenses.
2. At open enrollment, run the same big event through every plan you're considering. HDHP plans look cheaper on premium but can be much more expensive in a max-out year — the right comparison is total annual cost (premium + worst-case OOP).
3. If you're eligible for an HSA, model the after-tax savings using the HSA Optimizer. Paying medical bills with pre-tax HSA dollars effectively shrinks the patient cost by your marginal tax rate.
4. Before a scheduled procedure, ask your provider's billing office for the allowed amount (not the billed charge) and your good-faith estimate required under the No Surprises Act. Plug the real number in here.
5. If the worst-case number scares you, the lever is usually emergency fund size, not insurance — see the Emergency Fund calculator.