Unjust Enrichment Refund Calculator

What is the Unjust Enrichment Return Calculator?

The Unjust Enrichment Return Calculator computes the amount to be returned when one party has obtained a financial benefit without a legal basis at the expense of another.
It covers common situations such as duplicate or double payments, mistaken bank transfers requiring civil recovery, void or cancelled contracts requiring restitution, and salary or fee overpayments.
The calculator reflects the distinction drawn in Article 748 of the Korean Civil Act between good-faith and bad-faith recipients, and shows both scenarios side by side so you can compare the amounts.

Article 741 of the Korean Civil Act states: “A person who obtains a benefit from another’s property or labor without any legal basis, thereby causing loss to the other, shall return such benefit.”
In addition to the principal, the calculator applies the applicable statutory interest rate — civil (5% p.a. under Civil Act Art. 379), commercial (6% p.a. under Commercial Act Art. 54), or the litigation surcharge rate (12% p.a. under the Act on Special Cases Concerning the Expedition of Legal Proceedings Art. 3) — to compute the total claim amount in one step.

Korea-specific disclaimer: This calculator is based entirely on Korean law — specifically the Civil Act (Arts. 741, 748, 749, 379), the Commercial Act (Arts. 54, 64), and the Act on Special Cases Concerning the Expedition of Legal Proceedings (Art. 3).
It provides a reference estimate only and does not replace legal advice from a Korean attorney or judicial scrivener. Laws and court interpretations may change; always verify current rules before filing a claim.

Who is this for?

• Anyone who made a duplicate or double payment and wants to calculate the refund amount
• Parties whose contract was voided or cancelled and need to estimate the restitution owed
• People who sent money to a wrong bank account and want to quantify a civil recovery claim
• Businesses or individuals who overpaid wages, service fees, or taxes and need the excess amount
• Anyone preparing a demand letter or a statement of claim for unjust enrichment
• Individuals checking how much statutory interest accrues before and after court service of process

Good-Faith vs Bad-Faith Recipient — The Interest Differs

The most critical issue in any unjust enrichment claim is whether the recipient knew there was no legal basis for the benefit (bad-faith) or genuinely did not know (good-faith).
Article 748 of the Korean Civil Act draws a clear line between the two, with significantly different return obligations.

Good-Faith Recipient — Civil Act Article 748(1)

A good-faith recipient — one who did not know there was no legal basis — is required to return only the benefit to the extent it still exists at the time of the claim.
In principle, no interest is added to the amount owed by a good-faith recipient.

Important — court precedent on monetary benefits:
Korean courts presume that the existing benefit equals the full amount received when the unjust enrichment consists of money, absent special circumstances proving the money was spent.
Therefore, even a good-faith recipient of money is in practice required to return the full principal.

Exceptionally, if the recipient can affirmatively prove that the money was already spent and no benefit remains, the return obligation may be reduced accordingly.

Bad-Faith Recipient — Civil Act Article 748(2)

A recipient who knew there was no legal basis must return the benefit plus interest, and must also compensate any additional loss caused to the claimant.
Under Article 749(1), a person becomes a bad-faith recipient from the moment they learn that there is no legal basis for the benefit they hold.

Article 749(2) — Conversion to bad faith on losing the lawsuit:
Even a good-faith recipient is treated as bad-faith from the date the lawsuit was filed if they are found liable and lose the case.
This means interest accrues retroactively from the filing date once the court rules against the defendant.

Which Interest Rate Applies?

The applicable interest rate depends on the nature of the underlying transaction and the stage of the legal proceedings.
The calculator lets you choose among three rates; in practice, different rates often apply to different time periods within the same case.

Interest Rate Comparison

Category	Rate	Legal Basis
Civil statutory rate	5% p.a.	Civil Act Art. 379 — general unjust enrichment interest
Commercial statutory rate	6% p.a.	Commercial Act Art. 54 — commercial transactions
Litigation surcharge rate	12% p.a.	Expedition Act Art. 3 — from the day after court service

※ Common practice: the civil (5%) or commercial (6%) rate applies until the statement of claim is served on the defendant; 12% applies from the day after service until full payment.

Statute of Limitations — Act Before Your Right Expires

• General unjust enrichment: 10-year limitation period under Civil Act Article 162(1).
• Commercial unjust enrichment: A 5-year period may apply under Commercial Act Article 64 when the claim arises from a commercial act.
• The period begins when the right can be exercised — generally the date the unjust enrichment arose.
• Once the period expires, the other party may raise the statute of limitations as a defense and refuse repayment.
• A certified demand letter, a lawsuit, or a provisional attachment can interrupt the running of the limitation period.

How to Use

Step 1: Enter the principal to be returned

Enter the amount that was received without legal basis — the duplicate payment, the mistaken transfer amount, or the sum paid under a contract that is now void or cancelled.

Step 2: Enter the start date and the end date

Enter the date the unjust enrichment arose (date of the duplicate payment, the transfer, etc.) and the date to which you want interest calculated.
The number of days in the interest period is calculated automatically.

Step 3: Select the recipient type and interest rate

Choose good-faith (return of existing benefit; no interest in principle) or bad-faith (return with statutory interest added).
Then select the applicable rate: civil 5%, commercial 6%, or litigation surcharge 12%.

Step 4: Read the result and use it

The total of principal plus accrued interest is computed automatically.
Use this figure as a reference for demand letters, court filings, or settlement negotiations.

Worked Examples

Example 1 — Duplicate payment of KRW 5 million

A vendor accidentally transfers KRW 5 million in payment twice for the same invoice.
The second transfer is received without a legal basis under Civil Act Article 741, and the recipient must return it.

Principal: KRW 5,000,000 / Enrichment date: 1 March 2024 / Calculation date: 1 March 2025
Civil rate 5% p.a. → Interest: KRW 250,000
Total claimable amount: KRW 5,250,000

If the recipient is found to be bad-faith, or if the 12% surcharge rate applies after service of the statement of claim, the total amount grows further.

Example 2 — Mistaken bank transfer (civil recovery)

A person accidentally transfers KRW 3 million to the wrong bank account.
The unintended recipient holds the money without legal basis and must return it through a civil unjust enrichment claim under Civil Act Article 741.

⚠️ Separate from the KDIC administrative program: Korea’s Deposit Insurance Corporation (KDIC) operates a separate administrative “Mistaken Transfer Return Support” program.
This calculator covers the civil law return amount (principal + statutory interest) under Civil Act Article 748, not the administrative support program.

Example 3 — Contract voided or cancelled

If a sales contract is cancelled due to fraud or mistake under the Civil Act, the legal basis for all amounts already paid disappears retroactively.
The buyer can claim back the full deposit, interim payment, and balance — plus statutory interest from the date of each payment — under Civil Act Article 741.

Where the contract was void from the outset (e.g., for violating a mandatory rule of law), the obligation to return arises from the very date the payment was made.

Example 4 — Overpayment or accounting error

When wages, service fees, or tax refunds are paid in excess of the correct amount, the excess constitutes unjust enrichment claimable under Civil Act Article 741.
Business-to-business overpayments typically attract the commercial statutory rate (6% p.a.) rather than the civil rate (5% p.a.).

⚠️ Distinct from excess contractual interest refunds: Claims for the return of interest charged above the cap set by the Interest Limitation Act are handled by a separate calculator — the “Contractual Interest / Interest Limitation Act Refund Calculator.”

Frequently Asked Questions

Q. Does a good-faith recipient have to pay interest?

A. Under Civil Act Article 748(1), a good-faith recipient must return only the existing benefit and does not owe interest in principle.
However, Korean courts presume that the existing monetary benefit equals the full amount received, absent proof that the money was spent. So in practice, a good-faith recipient of money is still required to return the full principal.

Q. Is recovery impossible once the limitation period expires?

A. You can still file a claim after the limitation period, but the other party may raise the statute of limitations as a defense and refuse to pay.
The general period is 10 years (Civil Act Art. 162) and the commercial period is 5 years (Commercial Act Art. 64). Act quickly — delay can forfeit your right to recover.

Q. When does the 12% litigation surcharge rate start?

A. Under Article 3 of the Act on Special Cases Concerning the Expedition of Legal Proceedings, 12% p.a. accrues from the day after the statement of claim is served on the defendant.
The civil (5%) or commercial (6%) rate applies to the period before service, so the two periods must be calculated separately and added together.

Q. Can I paste this result directly into a court filing?

A. This calculator is a reference estimation tool only.
For an actual statement of claim, the interest periods, good-faith or bad-faith determination, and any additional loss items must be carefully reviewed with a Korean attorney or judicial scrivener.

Q. What is the difference between civil and commercial unjust enrichment?

A. When the unjust enrichment arises from a commercial act — for example, a business-to-business transaction — the commercial statutory rate of 6% p.a. (Commercial Act Art. 54) and a 5-year limitation period (Commercial Act Art. 64) apply.
For a general civil unjust enrichment claim between private individuals, the defaults are 5% p.a. (Civil Act Art. 379) and a 10-year limitation period.

Q. Does the same rule apply if the recipient is a corporation?

A. Yes. Civil Act Article 741 applies equally regardless of whether the recipient is an individual or a corporation.
However, if the transaction qualifies as a commercial act between businesses, the commercial rate and the shorter limitation period are more likely to apply.

Practical Tips and Cautions

Send a certified demand letter (내용증명): Sending a formal demand by certified mail establishes the date of notice clearly and can be used to show when bad faith began, strengthening your claim.
Keep payment records: Bank transfer confirmations and card receipts serve as key evidence for duplicate-payment or mistaken-transfer claims. Preserve them carefully.
Record the service date precisely: Because the 12% surcharge rate starts the day after the statement of claim is served, note the exact service date to compute interest correctly.
Interest is simple, not compound: Statutory interest in Korea is calculated on a simple basis unless the parties have agreed otherwise; compound interest is not permitted as a default.
Interrupt the limitation period early: A certified demand letter (최고), a lawsuit filing, or a provisional attachment order can interrupt the statute of limitations. If expiry is near, take legal action immediately.
Consult a legal professional before filing: This calculator provides a reference estimate. For the actual legal claim, consult a Korean attorney (변호사) or judicial scrivener (법무사).

Scope of This Calculator and Related Calculators

This calculator estimates the civil unjust enrichment return amount (principal + statutory interest) under Korean Civil Act Articles 741 and 748.
For the following related situations, a dedicated calculator is more appropriate.

• Mistaken transfer — KDIC administrative support: Claims processed through the Korea Deposit Insurance Corporation’s “Mistaken Transfer Return Support” program → use the Mistaken Transfer Return Calculator.
• Excess contractual interest — Interest Limitation Act refund: Return of interest charged above the statutory cap → use the Contractual Interest / Interest Limitation Act Refund Calculator.
• This calculator provides a reference estimate only. Consult a Korean attorney or judicial scrivener for actual legal proceedings.

Calculate your unjust enrichment return amount now

Enter the principal, the date the enrichment arose, and the recipient type to get the total return amount — principal plus interest — instantly.

Use the result as a reference before sending a demand letter, filing a lawsuit, or entering settlement negotiations with the other party.

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