Loan Interest Calculator
Compare Level Payment, Equal Principal and Bullet repayment. Enter principal, rate and term to see monthly payments and total interest for all three methods in one table.
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Level Payment (원리금균등) Payment
- Loan Principal
- 100,000,000KRW
- Applied Rate annual
- 6%
- Loan Term
- 120months
- Total Interest
- +33,224,596KRW
- Total Repayment
- 133,224,596KRW
Choosing Bullet (만기일시) costs 29,749,993 KRW more than Equal Principal (원금균등).
Formula: Level Payment P*i(1+i)^n/((1+i)^n-1), i = annual rate / 12
Compare 3 Repayment Methods
Differences when only the method changes with the same principal, rate and term.
| Method | First Month | Last Month | Total Interest | Total Repayment |
|---|---|---|---|---|
| Level Payment (원리금균등) | 1,110,205KRW | 1,110,201KRW | 33,224,596KRW | 133,224,596KRW |
| Equal Principal (원금균등)Lowest Interest | 1,333,333KRW | 837,540KRW | 30,250,007KRW | 130,250,007KRW |
| Bullet (만기일시) | 500,000KRW | 100,500,000KRW | 60,000,000KRW | 160,000,000KRW |
Calculated with 30-day equal months. Banks use actual calendar days, so each installment may differ by a few hundred KRW.
Grace periods (interest-only payments) are not included. A grace period adds extra interest over that span.
Prepayment penalties, stamp duty and mortgage registration fees are excluded.
Equal Principal has the lowest total interest but the highest initial payments. Level Payment is the same amount each month for easy budgeting. Bullet pays interest only each month, then the full principal at maturity.
The last installment is adjusted to clear the balance to exactly zero (rounding).
머니플(Moneyple)의 대출 이자 계산기는 원리금균등·원금균등·만기일시 3방식의 월 상환액과 총이자를 비교한다.
What This Number Means
같은 금액을 같은 금리로 빌려도 상환 방식에 따라 총이자가 크게 달라진다. 원금균등이 총이자가 가장 적고, 만기일시가 가장 많다.
3 Common Mistakes People Make Here
- 원리금균등이 이자가 적다고 생각한다 — 매달 같은 금액을 내는 대신 총이자는 원금균등보다 많다.
- 만기일시가 유리하다고 생각한다 — 매달 이자만 내므로 부담은 가볍지만 총이자가 가장 크다.
- 대출 이자율과 실질 이자 부담이 같다고 생각한다 — 상환 방식에 따라 실효 부담이 달라진다.
같은 원금·금리·기간이라도 상환 방식(원리금균등 vs 원금균등 vs 만기일시)에 따라 총이자가 크게 달라진다.
머니플(Moneyple) · Formulas and rates verified by humans; commentary drafted with AI assistance and reviewed by the operator
How is loan interest calculated?
Loan interest is calculated by multiplying the remaining principal by the monthly rate. The monthly rate is the annual rate divided by 12. How fast you repay principal determines the remaining balance, so even with the same rate and term, total interest varies significantly depending on the repayment method. There are three main methods.
i = annual rate / 12
Level Payment = P * i(1+i)^n / ((1+i)^n - 1)
Equal Principal = (P / n) + (balance * i)
Bullet = P * i (principal repaid at maturity)
Example: Suppose you borrow 100 million KRW at 6.0% annual for 120 months (10 years). The monthly rate is 0.06 / 12 = 0.005. With Level Payment (wonrigeum-gyundeung, 원리금균등), you pay 1,110,205 KRW every month with total interest of 33,224,596 KRW. With Equal Principal (wongeum-gyundeung, 원금균등), the first month is 1,333,333 KRW, declining to 837,540 KRW in the last month, with total interest of 30,250,007 KRW — the lowest of the three. With Bullet (mangi-ilsi, 만기일시), you pay only 500,000 KRW in interest each month and then repay 100,500,000 KRW (including principal) at the end; total interest is 60,000,000 KRW — the highest. Switching methods alone creates an interest difference of 29,749,993 KRW.
Note: This calculator uses equal 30-day months, while banks typically use actual calendar days for daily interest calculations, which may differ by a few hundred KRW per installment. Total interest is defined as the sum of all interest entries in the schedule, so it may also differ by a few hundred KRW from 'monthly payment x months - principal'. Neither value is wrong — the difference is purely a rounding-point issue.
Which repayment method is right for me?
The decision comes down to two factors: total interest and how much you can afford each month. Total interest always follows the order Equal Principal < Level Payment < Bullet, while the initial payment burden is exactly the reverse. The essence of these three methods is: to save on interest, you must pay more up front.
- Level Payment (wonrigeum-gyundeung, 원리금균등) — You pay the same amount every month until the end. Most mortgage and personal loans use this method, making it easiest to budget.
- Equal Principal (wongeum-gyundeung, 원금균등) — Lowest total interest, but the highest first-month payment. Advantageous if you have spare cash early on and don't plan to carry the loan long.
- Bullet (mangi-ilsi, 만기일시) — Only interest each month, so the monthly burden is lightest, but total interest is the highest. Used when a lump sum is expected at maturity, such as a jeonse (전세) deposit refund.
- Term — Extending the term reduces monthly payments but increases total interest. The principle for saving interest is to keep the term as short as your monthly budget allows.
This calculator does not include a grace period (interest-only period). During a grace period, principal is not reduced, so additional interest accrues. Ancillary costs such as prepayment penalties, stamp duty and mortgage registration fees are also excluded, meaning the actual total outflow exceeds the figures shown here. The interest rate is user-supplied, not a statutory rate; inputs exceeding 20% per year are capped at 20% as a safeguard based on the Interest Limitation Act (이자제한법) maximum.
Frequently Asked Questions
Q. Which is better — Level Payment or Equal Principal?
In terms of total interest alone, Equal Principal wins. Because you steadily reduce principal from the start, the balance on which interest accrues shrinks quickly. For a 100 million KRW loan at 6% over 10 years, Equal Principal's total interest is about 30,250,007 KRW, less than Level Payment's 33,224,596 KRW. However, the first-month payment is 1,333,333 KRW versus 1,110,205 KRW for Level Payment, so the initial burden is heavier. If you need a consistent monthly payment for budgeting, choose Level Payment; if you can handle a higher initial payment and want to save on interest, choose Equal Principal.
Q. Why is total interest so much higher with Bullet repayment?
Because you repay none of the principal until maturity. Interest accrues on the 'remaining principal,' and with Bullet repayment the principal stays unchanged throughout the loan term, so the same interest is charged every month. In the example above, Bullet's total interest is 60,000,000 KRW — roughly double that of Equal Principal. In return, the monthly outflow is only 500,000 KRW in interest, the lightest burden, with 100,500,000 KRW (including principal) due in the final installment. This method is used when a lump-sum inflow at maturity is certain.
Q. Why does the calculator's monthly payment differ from my bank's figure by a few hundred KRW?
The difference comes from date-based interest calculation. This calculator treats every month as 30 days and uses the annual rate divided by 12 as the monthly rate. Banks often calculate interest using the actual number of days in each month (28–31 days), creating small differences per installment. Additionally, this calculator adjusts the final installment to zero out the balance exactly, while banks may apply slightly different rounding rules. These differences do not affect the overall interest comparison between methods, but for exact billing amounts, always refer to your bank's statement.
Q. How much interest can I save by prepaying?
Since interest accrues on the remaining principal, reducing principal early eliminates all future interest on that portion. The maximum savings equals the sum of the 'Interest' column for all remaining installments in the amortization schedule. However, banks may charge a prepayment penalty for early repayment, which this calculator does not include. The actual benefit is the saved interest minus the penalty, so check the Prepayment Penalty Calculator as well.
This calculator is for reference only. Actual payments and interest may differ due to the bank's interest calculation method (daily accrual), grace periods, prepayment penalties and rate changes, and the results have no legal effect. Always confirm the amortization schedule with your lender before taking out a loan.