Korea Payroll & Tax API › late-payment-interest

South Korea statutory late-payment interest (jiyeon sonhaegeum) on a money debt

South Korea statutory late-payment interest (jiyeon sonhaegeum) on a money debt: 5% civil, 6% commercial, 12% under the litigation-promotion act after a complaint is served, or a contract rate, prorated by day.

Price: $0.05 USDC per call over REST (x402 on Base, no API key). MCP: paid-only — the MCP tool returns payment instructions. Basis year: 2026.

Input

Field	Type	Required	Description
`principal`	number	yes	Unpaid principal (KRW)
`startDate`	string	yes	First day interest accrues (YYYY-MM-DD)
`endDate`	string		Last day counted; default today (YYYY-MM-DD)
`rate`	civil \| commercial \| litigation \| custom		civil 5% (default), commercial 6%, litigation 12%, or custom
`customRatePct`	number		Annual rate in percent when rate is custom

Example request

curl -X POST https://api.kkuldogu.com/v1/late-payment-interest -H "content-type: application/json" \
  -d '{"principal":10000000,"startDate":"2026-01-01","endDate":"2026-10-31","rate":"litigation"}'

Without payment this returns 402 with x402 payment requirements; an x402 client pays $0.05 USDC and retries.

Example response

{
  "basisYear": 2026,
  "currency": "KRW",
  "disclaimer": "For reference only, not legal, tax or financial advice. Computed from South Korean statutes and standard formulas as of 2026; reliefs, exemptions and special cases not shown in the result are not modeled, and rules may have changed. Confirm with the relevant office, court, lender or a professional before acting.",
  "source": "https://kkuldogu.com",
  "tool": "late-payment-interest",
  "input": {
    "principal": 10000000,
    "startDate": "2026-01-01",
    "endDate": "2026-10-31",
    "rate": "litigation"
  },
  "result": {
    "interest": 999452,
    "days": 304,
    "annualRatePct": 12,
    "totalDue": 10999452,
    "perDay": 3288
  }
}

For reference only, not legal or tax advice. Uses official 2026 Korean rates and the same formulas as the kkuldogu.com calculators; actual payroll, NHIS/NPS notices and tax settlement can differ. · Calculators for people (Korean): kkuldogu.com · API home · llms.txt · OpenAPI