Loan Interest Calculator

Estimate monthly payment, total interest, and total repayment across common loan repayment methods.

Loan inputs

Compare monthly payment and interest by repayment method.

Estimated monthly payment

$497

Total interest

$4,844

Total repayment

$29,844

First to last payment

$497 / $497

Equal principal usually lowers total interest but starts with a higher payment. Interest-only loans defer principal and create a larger final payment.

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What is the loan interest calculator?

This calculator compares monthly payments, total interest, and repayment schedules for credit loans, overdrafts, card loans, car installment loans, and similar borrowing. It preserves the Korean distinction between equal principal and interest, equal principal, and bullet repayment.

Repayment methods

Equal principal and interest

  • Monthly payment = principal x monthly rate / (1 - (1 + monthly rate)^(-period)).
  • The payment is fixed, but the early months contain a larger interest portion and a smaller principal portion.
  • This method is easy for household budgeting because the monthly burden is stable.

Equal principal and bullet repayment

  • Equal principal repayment uses monthly principal = principal / period, then adds interest on the remaining balance.
  • Equal principal repayment can reduce total interest by about 10% to 15%, but the first payment can be 30% to 40% higher.
  • Bullet repayment pays only interest during the period and repays principal at maturity. It has the lowest monthly burden but the highest total interest.
  • Overdrafts and short operating loans often behave like interest-only or bullet structures until repayment.

Interest-saving strategy

Ways to reduce interest

  • Compare several lenders because a 0.5 to 2.0 percentage point rate gap can dominate small fee differences.
  • Use the rate reduction request right after a credit-score upgrade, income increase, promotion, longer tenure, or debt reduction.
  • Check preferential-rate conditions such as salary transfer, automatic debit, card spending, and app-only products.
  • Consider government or policy products before card loans or high-rate second-tier loans.
  • Prepayment can be useful when the interest saving exceeds the prepayment fee.

Fees and tax notes

  • Prepayment fees are often around 1% to 2% and are commonly waived after 3 years, although many unsecured products have no fee.
  • Equal principal repayment lowers total interest but requires more cash flow early in the schedule.
  • Fixed rates provide payment certainty, while variable rates can benefit if market rates fall but create risk if rates rise.
  • Mortgage interest income deduction can apply up to KRW 18,000,000 under qualifying Korean rules, while ordinary credit-loan interest is generally not deductible.