Loan Calculator Guide: Accurately Calculate Interest and Repayment
2025-01-09
1. Loan Interest Calculation Methods
Loan interest is calculated in two main ways. ① Equal installment: Pay same amount (principal+interest) monthly. Interest proportion is high initially, principal proportion increases later. ② Equal principal: Pay same principal monthly, interest decreases with balance. Higher initial burden but lower total interest.
2. Equal Installment Calculation
Monthly payment = Loan amount × [Monthly rate × (1+Monthly rate)^Months / {(1+Monthly rate)^Months - 1}]. Example: 100M KRW, 4% annual, 20 years (240 months). Monthly rate = 0.04/12 = 0.00333. Monthly payment = 100,000,000 × [0.00333 × 1.00333^240 / (1.00333^240 - 1)] ≈ 606,000 KRW. Total repayment ≈ 145.44M KRW (interest 45.44M KRW).
3. Equal Principal Calculation
Monthly principal = Loan amount / Months. Monthly interest = Remaining principal × Monthly rate. Example: 100M KRW, 4% annual, 20 years. Monthly principal = 100,000,000 / 240 ≈ 416,667 KRW. 1st interest = 100,000,000 × 0.00333 ≈ 333,333 KRW. 1st payment = 750,000 KRW. Interest decreases monthly, last payment about 418,000 KRW. Total interest ≈ 40.08M KRW.
4. Which Repayment Method to Choose?
Equal installment: ① Easier budgeting with consistent monthly amount. ② Lower initial cash flow burden. ③ Suitable for long-term loans. Equal principal: ① Lower total interest burden. ② Higher initial payment requires reserve funds. ③ Beneficial for early repayment plans or stable income.
5. Interest Reduction Methods
① Compare rates: Compare multiple institutions for lowest rate. ② Manage credit score: Higher score gets preferential rates. ③ Early repayment: Partial prepayment reduces interest. ④ Refinancing: Switch to lower rate loan. ⑤ Variable vs fixed rate: Choose based on rate outlook. ⑥ Utilize government-supported loans.
6. Pre-loan Checklist
① Total loan limit: DTI (Debt-to-Income) 40% or less recommended. ② Check DSR (Debt Service Ratio). ③ Prepayment penalty terms. ④ Grace period utilization. ⑤ Additional costs (handling fees, stamp duty). ⑥ Rate change scenario simulations. ⑦ Accurate repayment ability assessment.