korean-financial-calculators

Pure TypeScript Korean financial calculators with 2026 tax rates and insurance premiums.

Zero dependencies. Framework-agnostic. Works in Node.js and browsers.

Extracted from t2value.com.

Install

npm install korean-financial-calculators

Calculators

1. Net Salary — 연봉 실수령액

Calculates monthly take-home pay after 4 major insurances (NPS, NHI, LTC, EI) and income tax.

import { calculateNetSalaryKR } from 'korean-financial-calculators';

const result = calculateNetSalaryKR({
  grossAnnual: 50_000_000,
  nonTaxableMonthly: 200_000,
  dependents: 1,
});

result.grossMonthly;    // → 4_166_666
result.netMonthly;      // → 3_490_134
result.effectiveRate;   // → 16.24 (%)
result.insurance;       // → { nps: 188_416, nhi: 142_600, ltc: 18_730, ei: 35_699, totalInsurance: 385_445 }
result.tax;             // → { incomeTax: 264_625, localTax: 26_462, totalTax: 291_087, ... }
result.monthlyBreakdown // → [{ key: "gross", amount: 4_166_666, ... }, ...]

Input

Field	Type	Description
grossAnnual	number	Annual salary in KRW
nonTaxableMonthly	number	Monthly non-taxable amount (e.g. meal allowance)
dependents	number	Number of dependents including self

---

2. Hourly Wage — 시급 계산기

Converts between hourly/monthly/annual wages. Compares against 2026 minimum wage (₩10,320).

import { calculateHourlyWageKR } from 'korean-financial-calculators';

const result = calculateHourlyWageKR({
  mode: 'monthly',
  amount: 2_500_000,
  overtimeHours: 5,
});

result.hourlyWage;      // → 11_961
result.dailyWage;       // → 95_688
result.monthlyWage;     // → 2_499_849
result.annualWage;      // → 29_998_188
result.overtimePay;     // → 389_779
result.totalMonthly;    // → 2_889_628
result.isAboveMinimum;  // → true
result.minimumWageDiff; // → 1_641

Input

Field	Type	Description
mode	'hourly' | 'monthly' | 'annual'	Input mode
amount	number	Wage amount matching the mode
overtimeHours	number	Weekly overtime hours

---

3. Severance Pay — 퇴직금

Calculates severance per Korea Labor Standards Act Article 34.

import { calculateSeverance } from 'korean-financial-calculators';

const result = calculateSeverance({
  monthlyPay: 3_000_000,
  yearsWorked: 5,
  monthsWorked: 6,
});

result.severancePay;    // → 16_278_003
result.dailyAvgWage;    // → 98_630
result.totalDays;       // → 2_008
result.monthsEquivalent // → 5.4
result.perYear;         // → 2_959_637
result.isUnderOneYear;  // → false
result.timeline;        // → [{ year: 1, cumulativePay: 2_958_900 }, ...]

Input

Field	Type	Description
monthlyPay	number	Monthly base pay in KRW
yearsWorked	number	Years of service
monthsWorked	number	Additional months (0–11)

---

4. Loan Interest — 대출이자

Three repayment methods: equal payment (원리금균등), equal principal (원금균등), bullet (만기일시).

import { calculateLoan, calculateEarlyPayoff } from 'korean-financial-calculators';

const input = {
  loanAmount: 100_000_000,
  annualRate: 4.5,
  loanMonths: 240,
  repaymentType: 'equal' as const,
};

const result = calculateLoan(input);

result.monthlyPayment;  // → 632_649
result.totalInterest;   // → 51_835_918
result.totalRepayment;  // → 151_835_918
result.schedule;        // → [{ month: 1, principal: 257_649, interest: 375_000, payment: 632_649, balance: 99_742_351 }, ...]
result.yearlyBreakdown; // → [{ year: 1, principalSum: 3_156_361, interestSum: 4_435_427, endBalance: 96_843_640 }, ...]

// Early payoff simulation
const earlyPayoff = calculateEarlyPayoff(input, 500_000);

earlyPayoff.originalMonths;  // → 240
earlyPayoff.reducedMonths;   // → 108
earlyPayoff.savedInterest;   // → 30_159_405

Input

Field	Type	Description
loanAmount	number	Loan amount in KRW
annualRate	number	Annual interest rate (%)
loanMonths	number	Loan term in months
repaymentType	'equal' | 'principal' | 'maturity'	Repayment method

Additional functions:

• calculateEarlyPayoff(input, extraMonthly) — Simulates early payoff with extra monthly payments
• calculateLoanScenarios(input, rates) — Compares results across different interest rates
• formatKRW(n) / formatKRWCompact(n) — Format numbers as "1,000,000" or "100만"

---

5. Weekly Holiday Pay — 주휴수당

Calculates weekly holiday allowance per Labor Standards Act Article 55. Eligible when working 15+ hours/week.

import { calculateWeeklyHolidayPay } from 'korean-financial-calculators';

const result = calculateWeeklyHolidayPay({
  hourlyWage: 10_320,
  weeklyHours: 40,
});

result.isEligible;          // → true
result.weeklyHolidayHours;  // → 8
result.weeklyHolidayPay;    // → 82_560
result.monthlyHolidayPay;   // → 358_723
result.effectiveHourlyWage; // → 12_384
result.monthlyTotal;        // → 2_152_339
result.employerMonthlyCost; // → 2_152_339

Input

Field	Type	Description
hourlyWage	number	Hourly wage in KRW
weeklyHours	number	Contracted weekly working hours

2026 Data Constants

All tax rates, insurance premiums, and thresholds are exported:

import {
  INSURANCE_RATES,
  INCOME_TAX_BRACKETS,
  MINIMUM_WAGE,
  SEVERANCE_DAYS,
  DEFAULT_LOAN_KR,
  WEEKLY_HOURS_THRESHOLD,
} from 'korean-financial-calculators';

INSURANCE_RATES.nps;     // → 0.0475 (4.75%)
INSURANCE_RATES.nhi;     // → 0.03595 (3.595%)
INSURANCE_RATES.ltcRate; // → 0.1314 (13.14% of NHI)
INSURANCE_RATES.ei;      // → 0.009 (0.9%)

MINIMUM_WAGE;            // → 10_320
WEEKLY_HOURS_THRESHOLD;  // → 15

Data Sources

Calculator	Source	Year
Net Salary	NTS 간이세액표, 소득세법, 4대보험 고시	2026
Hourly Wage	고용노동부 최저임금 고시	2026
Severance	근로기준법 제34조, 근로자퇴직급여보장법 제8조	2026
Loan	Pure math	—
Weekly Holiday Pay	근로기준법 제55조, 시행령 제30조	2026

License

MIT