How the payment is worked out
PMT = P × i ÷ (1 − (1 + i)^−N). P is the amount borrowed, i is the rate for one payment period — the APR divided by the number of payments a year, which is the US consumer-loan convention — and N is the number of payments. Borrow 200,000 at 6% over 30 years and i = 0.005, N = 360, so the payment is 1,199.10 a month.
Each payment is then split: interest first, principal with what is left. Payment 1 on that loan is 1,000.00 interest and 199.10 principal — 83% of the money goes to the lender. Payment 360 is 5.97 interest and 1,194.17 principal, and its total is 1,200.14 rather than 1,199.10 because the final row absorbs every rounding remainder so the balance lands exactly on zero.
Because the schedule is built row by row and the totals are the sum of those rows, "total interest" always equals the sum of the interest column you can see. Total interest on this loan is 231,677.04 — more than the 200,000 borrowed, which is normal for a 30-year term at 6%.
Reading the amortization schedule
The interest share of each payment falls as the balance falls, so the split moves slowly from mostly-interest to mostly-principal. On the 200,000 loan at 6%, the balance does not reach half — 100,000 — until payment 252, which is year 21 of 30. Two thirds of the calendar has to pass before half the debt is gone.
This is why the payoff figure you get from the lender is higher than "payment × payments remaining ÷ something": the outstanding balance is a present value, not a straight-line fraction. The Payment view of the table gives you the exact balance after every single payment, and the Annual view groups it into years with interest, principal and closing balance per year.
Fill in a first payment date and every row gets a real date, so the payoff date at the top is the month you actually finish. Copy table and Download CSV export exactly what is on screen, dates included.
Equal payment vs equal principal vs interest-only
This calculator computes the equal-payment (level payment, 원리금균등) loan, the standard everywhere for car, personal and student loans. The two alternatives change the numbers a lot, and Korean lenders offer all three. Borrowing 30,000 at 7% over 5 years:
- Equal payment (원리금균등) — 594.04 every month, total interest 5,642.12.
- Equal principal (원금균등) — principal is a flat 500 a month plus interest on the balance, so the first payment is 675.00 and the last is 502.92. Total interest is 5,337.50, about 305 less, but you pay 81 more in month one.
- Interest-only until maturity (만기일시상환) — 175.00 a month and the whole 30,000 at the end. Total interest 10,500, nearly double, because the balance never falls.
A grace period (거치기간), during which only interest is paid before the amortization starts, is not modelled here either. To approximate one, calculate the interest-only cost separately (balance × rate × grace years) and then run this calculator for the remaining term.
Monthly vs biweekly, and the “accelerated biweekly” trick
Switch the frequency to biweekly and the tool builds a genuine 26-payments-a-year loan: i = APR ÷ 26 and N = years × 26. On 30,000 at 7% for 5 years that is 273.81 every two weeks (130 payments) with 5,595.60 of interest, against 594.04 a month with 5,642.12. You pay 7,119.06 a year instead of 7,128.48 — the small gain comes from paying slightly sooner on average, not from paying more.
That is a different thing from the "accelerated biweekly" plan lenders market, where you pay half the monthly payment every two weeks — 26 half-payments is 13 monthly payments a year, so you quietly make one extra payment annually. To model that here, keep the frequency Monthly and put one twelfth of the payment in the extra field. On the 200,000 loan at 6%, an extra 99.93 a month finishes in 295 payments instead of 360 and saves 49,112 in interest.
Extra payments: how much they really save
The extra amount is applied to principal every period, which shortens the loan rather than lowering the payment. On 200,000 at 6% over 30 years (231,677.04 of interest at 1,199.10 a month):
- +100 a month — finishes at payment 295, five years early, saving 49,138.85.
- +200 a month — finishes at payment 252, nine years early, saving 79,800.86.
The saving is not proportional: doubling the extra payment from 100 to 200 adds only about 62% more saving, because the earliest extra payments are the ones that remove the most future interest. This is also the reason a lump sum in year 1 beats the same lump sum in year 10.
Two caveats the calculation cannot see. First, a prepayment penalty: Korean loans typically charge 중도상환수수료 of about 0.5–1.4% of the amount prepaid, tapering to zero after three years, and this tool does not deduct it — subtract it from the saving above before deciding. Second, some lenders apply extra money to future instalments instead of to principal unless you tell them otherwise, which produces none of this saving.
APR, interest rate and what the tool assumes
The number you type is applied directly to the balance. In the US, APR under the Truth in Lending Act also folds origination and broker fees into the quoted rate, so a 6.00% note rate with 2% of fees is advertised at a higher APR — the payment on your statement comes from the note rate, while the APR is the comparison figure. If fees are financed into the loan, add them to the amount rather than to the rate.
The rate is fixed for the whole term here. For a variable-rate loan — Korean 변동금리 products reset against COFIX every 6 or 12 months — run the calculation at the current rate and again at the rate cap, and read the two payments as a range. Insurance premiums, guarantee fees and stamp duty are not included either.
Input limits: term up to 50 years plus 0–11 months, at most 1,200 payments, and a rate from 0% to 1000%. A rate so low that the payment cannot cover the interest is rejected as negative amortization rather than silently producing a growing balance.
Typical terms by loan type
- Car loans — 36 to 84 months. Longer terms lower the payment but keep you underwater on the car for longer; at 84 months the balance can exceed the resale value for most of the loan.
- Personal / unsecured loans — 12 to 60 months, and the rate is the variable that matters far more than the term.
- Student loans — 10 to 25 years, often with a grace period that this calculator does not model (see the section above).
- 0% promotional / instalment plans — enter 0 as the rate and the payment is simply the amount divided by the number of payments: 25,000 over 5 years is 416.67 a month with zero interest, every cent of it principal. Compare that against the cash discount you give up, which is the real cost of a 0% offer.