High-Cost Medical Expense Benefit Calculator (Japan Kogaku Ryoyohi)
Enter your income category and monthly medical costs to estimate the out-of-pocket limit and refund amount under Japan's high-cost medical expense benefit system, based on the official formula shared by health insurance and national health insurance.
What is the high-cost medical expense benefit (Kogaku Ryoyohi)?
The high-cost medical expense benefit (高額療養費制度, "Kogaku Ryoyohi") is a public program under Japan's health insurance system. If your out-of-pocket medical costs incurred within a single calendar month exceed a set ceiling (the out-of-pocket limit), the excess amount is refunded to you by your health insurer. This rule applies uniformly regardless of which Japanese health insurance plan you're enrolled in — employees' health insurance run by the Japan Health Insurance Association (Kyokai Kenpo) or a company health insurance union, or the municipal National Health Insurance (Kokumin Kenko Hoken) — so that a sudden surgery, hospitalization, or extended course of treatment doesn't translate into an unbounded household expense.
The out-of-pocket limit is divided into five income categories based on age and income, and each category is calculated either as a flat amount or as "a flat amount plus a percentage add-on tied to total medical cost." This calculator only asks for your income category, your total monthly medical cost, and your co-payment rate, then automatically works out both the out-of-pocket limit and the refund you can expect — making it useful for planning funds ahead of a hospital stay or for double-checking a refund notice you've already received.
Sources used in this calculation
Statutory figures such as tax and insurance rates come from the public bodies listed below. They change when the law is revised, so please also check the primary source before relying on the result for an important decision.
- High-cost medical care out-of-pocket limit — Japan Health Insurance Association (全国健康保険協会・協会けんぽ) Effective 2026-08 to 2027-07 ／ Last checked 2026-09-09
How to calculate your high-cost medical benefit
- Select your income category Choose Category A through O based on your standard monthly remuneration or prior-adjusted income. If you're not sure which applies, check your pay slip or a tax withholding certificate.
- Enter your total monthly medical cost Enter the full amount shown on your hospital receipt before insurance coverage is applied — that is, your co-payment plus the amount your insurer paid.
- Select your co-payment rate Pick 10%, 20%, or 30% depending on your age and income bracket. Match this to the rate printed on your health insurance card.
- Check the result The calculator displays your out-of-pocket limit, the amount refunded under the high-cost medical benefit, and your final out-of-pocket cost after the refund.
Tips for getting more out of it
- Obtaining a "certificate of applicable limit" in advance caps your payment at the hospital counter to the out-of-pocket limit, so you don't need to wait for a separate refund application.
- Using your health insurance card linked to your My Number card (Mynaho Kenkosho) automatically caps your counter payment at the limit, even without a certificate of applicable limit.
- Applications for the high-cost medical benefit generally expire after 2 years, so check with your insurer promptly if you have unclaimed past medical expenses.
- The medical expense deduction (for tax filing) is based on your net cost after subtracting any high-cost medical benefit refund, so be careful about the order of calculation if you use both programs.
When to use this high-cost medical benefit calculator
Estimating costs before surgery or hospitalization
Once you receive a rough cost estimate for an upcoming procedure or hospital stay, entering it here shows how far your actual out-of-pocket burden will be capped, and helps you decide whether it's worth obtaining a certificate of applicable limit in advance.
Coordinating with the medical expense tax deduction
Because the medical expense deduction on your tax return is based on costs after subtracting any high-cost medical refund, working out your expected refund here first makes it much easier to estimate the deduction accurately.
Verifying a refund decision you've already received
After completing an expensive course of treatment, you can compare the refund amount your insurer actually decided on against this calculator's result to confirm it looks correct.
Forecasting a year when your income category might change
In a year when a raise, bonus change, or retirement is likely to shift your standard monthly remuneration, running the numbers under a different category in advance shows how your out-of-pocket limit would change.
Glossary of high-cost medical benefit terms
- High-cost medical expense benefit (高額療養費制度)
- A program under which, if your out-of-pocket medical cost for a single month exceeds the limit set for your income category, your health insurer refunds the excess amount to you.
- Standard monthly remuneration (標準報酬月額)
- Your salary rounded into a set of official brackets, used to determine social insurance premiums and your income category for this benefit. It is not the same figure as your raw pay slip amount.
- Prior-adjusted income (旧ただし書き所得)
- The income figure used by National Health Insurance to determine your category. It is calculated as your total income minus the basic deduction used for resident tax purposes.
- Certificate of applicable limit (限度額適用認定証)
- A certificate issued in advance by your health insurer that lets you pay only up to the out-of-pocket limit at the hospital counter, instead of paying the full amount and waiting for a refund.
- Out-of-pocket limit (自己負担限度額)
- The maximum amount you personally pay toward medical costs incurred in one month. It is set as either a flat amount or a flat amount plus an add-on tied to your total cost, depending on your income category.
- Household aggregation (世帯合算)
- A rule that combines the co-payments paid within one month by family members covered under the same health insurance policy; if the combined total exceeds the limit, the excess is refunded.
- Multiple-instance reduction (多数回該当)
- A rule that further lowers the out-of-pocket limit starting from the fourth time you receive the high-cost medical benefit within a rolling 12-month period.
FAQ
Side Note — Why the out-of-pocket limit uses a "fixed amount plus 1%" design
The out-of-pocket limit under the high-cost medical benefit system isn't a simple flat amount — it's a graduated formula of "fixed amount plus (medical cost minus threshold) times 1%." This design keeps the impact on insurance finances within a bounded range even as medical costs rise without limit, while also softening how much a patient's out-of-pocket cost grows. Because the extra burden is capped at 1% of any additional cost, patients receiving extremely expensive treatment — advanced medicine or long hospital stays — end up with an effectively lower burden ratio the more their costs rise.
The five-tier income category system exists to ensure fairness based on ability to pay. The January 2015 reform split what had been 3 categories for those under 70 into 5, raising the limit for higher-income earners while giving more consideration to lower-income households. The reform aimed to balance the sustainability of insurance finances with income redistribution amid rising medical costs from an aging population.
The advance "certificate of applicable limit" procedure emerged because the high-cost medical benefit originally only worked as a reimbursement — patients paid the full amount at the counter and applied afterward for a refund. This became a social problem, as patients undergoing surgery or hospitalization had to temporarily cover hundreds of thousands of yen out of pocket. The certificate system, and now integration with the My Number health insurance card, let patients cap their counter payment at the limit itself, greatly easing that temporary financial burden.