The same loan can cost very different amounts of interest depending on how you repay it. Enter the loan amount, annual rate, and term to calculate the monthly payment, total interest, and a full payment schedule for annuity, equal-principal, and bullet repayment.
Annuity keeps the combined payment of principal and interest the same every month, which makes budgeting easy, though interest makes up most of the early payments. Equal principal repays the same amount of principal each month, so payments start at their largest and shrink; the balance falls fastest and the total interest is the lowest. Bullet repayment pays interest only until the end, when the whole principal is repaid at once — the smallest monthly outlay but the highest total interest. The repayment method guide compares all three with worked examples.
Each month's interest is the remaining balance multiplied by the annual rate divided by 12. Amounts are rounded to whole units, and any rounding remainder is settled in the final payment. During a grace period only interest is paid and the principal does not decrease. Prepayment penalties, guarantee fees, and daily interest calculations are not included.
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Q. What is the difference between annuity and equal-principal repayment?
With annuity repayment, the total monthly payment (principal plus interest) stays the same every month. With equal-principal repayment, you repay the same amount of principal each month, so the payment starts larger and shrinks over time. For the same amount, rate, and term, equal principal costs less total interest because the balance falls faster. On a 100,000,000 loan at 4% for 10 years, total interest is about 21,490,000 with annuity and about 20,170,000 with equal principal.
Q. How much extra interest does a grace period add?
During a grace period you pay interest only and the principal does not shrink, so that period's interest is added in full. Borrowing 50,000,000 at 5% with a one-year grace period adds roughly 2,500,000 of grace-period interest, and the payments afterwards also rise because the remaining term is shorter. A grace period trades lower payments now for higher total cost.
Q. When is bullet repayment used?
With bullet repayment you pay only interest each month and repay the entire principal at maturity. It appears in some deposit-backed (jeonse) loans and short-term business financing. The monthly outlay is the smallest of the three methods, but because the principal never shrinks, the total interest is the highest. It only makes sense when repaying the full principal at maturity is certain.
Q. Are prepayment penalties included in the calculation?
No. This calculator covers principal and interest only. Prepayment penalties, guarantee fees, and stamp duties vary by product, so check the terms of your lender before taking out or prepaying a loan.
Q. Why does my result differ slightly from my bank's app?
Lenders differ in how they round sub-unit amounts and whether the first period's interest is calculated daily, which can shift results by a few hundred to a few thousand units. This tool applies monthly calculation with whole-unit rounding as a reference; your lender's amortization schedule is the authoritative figure.