Loan Interest Calculator
Calculate monthly loan repayments and total interest across different repayment methods. Includes DSR diagnosis.
This calculator is for reference only and may differ from actual amounts due to law changes or individual circumstances. Please consult a licensed professional (tax accountant, labor attorney, etc.) for accurate calculations.
= 1.0 billion won
During the grace period, only interest is paid.
Monthly Payment
506,685
Total Interest
82,406,715
Total Payment
182,406,600
Interest-to-Principal Ratio
82.4%
Diagnosis
Total interest is 82% of principal — consider a shorter term or lower rate. | DSR 40% guideline: Recommended monthly income ≥ $1,266,713
Payment Composition
Monthly Payment Trend
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Frequently Asked Questions
Q. What is the difference between equal-principal-and-interest and equal-principal repayment?
Equal P&I pays the same total amount each month (principal + interest). Equal principal repays the same principal each month with decreasing interest, resulting in lower total interest but higher initial payments.
Q. What is a bullet (balloon) repayment?
With bullet repayment, you pay only interest each month and repay the full principal at maturity. Monthly payments are lower but total interest is highest, and you need a lump sum at maturity.
Q. What is the DSR 40% regulation?
DSR (Debt Service Ratio) is the ratio of all annual loan repayments to annual income. New bank loans are restricted when DSR exceeds 40% (50% for non-bank lenders).
Q. What is a grace period?
A grace period is an initial period where you pay only interest with no principal repayment. After the grace period ends, you repay both principal and interest. It lowers initial payments but increases total interest.
Q. Which is better — fixed or variable rate?
Fixed rates are better during rising rate environments; variable rates are better when rates are falling. For stability, fixed rates are generally recommended.
Q. Can I change repayment methods mid-loan?
Most banks allow repayment method changes, but early repayment fees may apply. Typically 1–1.5% of principal is charged if repaid within 3 years of the loan date.
How to Use
Choose: Equal P&I (same monthly payment), Equal Principal (same principal, decreasing interest), or Bullet (interest only until maturity).
Input loan amount, annual interest rate (%), and loan term (years). Set a grace period if needed.
Monthly payment, total interest, and total repayment are shown instantly. Also see the principal-to-interest ratio and recommended income based on DSR.
Use the pie chart for principal/interest breakdown and the bar chart for monthly repayment trends. The detail table shows monthly principal, interest, and balance.
Expert Knowledge: Loan Interest Calculator
Loan interest calculation is fundamental financial knowledge applied to mortgages, personal loans, auto financing, and more. As of 2024, Korea's household debt exceeds ₩1,886 trillion — over 100% of GDP — making individual loan size management critical.
Equal P&I (annuity method) uses the PMT formula: PMT = P × r(1+r)^n / ((1+r)^n - 1), where P = principal, r = monthly interest rate, n = total repayment months. Equal principal repayment adds fixed monthly principal (P/n) to balance-based interest, resulting in higher initial payments but 10–15% less total interest than equal P&I.
Korea's DSR regulation (since 2022) limits new loans when the Debt Service Ratio exceeds 40% for bank lenders and 50% for non-bank lenders. Student loans, auto installments, and credit card installments are all included in DSR calculations. Use this calculator's DSR diagnosis feature to verify your borrowing capacity before applying.
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