When Does Refinancing a Loan Pay Off? A Break-Even Framework
A one-percentage-point rate drop sounds like an obvious win. But once you subtract prepayment penalties and setup fees, the result can tip either way. This guide gives a rough first-pass formula and three hypothetical scenarios. A final decision requires both loans' actual amortization schedules and every switching cost.
1. Hidden Costs of Refinancing
- Prepayment penalty — varies by contract date, product, repayment date, and waiver; obtain the lender's payoff quote
- Appraisal & mortgage fees — confirm appraisal, registration, release, and which party pays each item
- Stamp duty, legal, and other fees — use the actual quote and any product-specific waiver
2. Interest-Only First-Pass Formula
Break-even months = Total switching cost ÷ (Old monthly interest − New monthly interest)
Using each loan's first-month interest can screen loans whose balances and structures are broadly comparable. It is not a profit test for amortizing loans: balances and interest decline, and a different term or repayment method changes both monthly payments and total interest. A result shorter than the remaining term does not, by itself, prove a net gain.
3. Three Hypothetical First-Pass Scenarios
All fees below are illustrative assumptions, not current quotes for a particular lender. Replace them with the payoff amount, execution costs, rate type, term, and repayment method offered to you.
A) Mortgage 200M, 15 years remaining, 4.8% → 3.5%
- Prepayment penalty: 2.4M
- Other fees: ~0.6M → Total: 3.0M
- Monthly interest gap: ~217K
- First-month-interest approximation: ~14 months
This is a prompt to compare full schedules, not proof that refinancing is profitable.
B) Unsecured loan 30M, 2 years remaining, 6.2% → 5.3%
- Total switching cost: ~0.35M
- Monthly gap: ~22.5K
- Approximate screen: 15.5 months out of 24
The result is close enough to the remaining term that actual schedules and quotes can reverse it.
C) Mortgage 150M, 3 years remaining, 4.2% → 3.6%
- Total switching cost: ~2.3M
- Monthly gap: ~75K
- Approximate screen: 31 months out of 36
This approximation alone cannot support a recommendation.
4. Compare Full Cash Flows
There is no universal "two-thirds of the remaining term" decision rule. Compare the old loan's remaining principal-and-interest payments with all payments and switching costs under the new loan on the same date basis. Model fixed versus floating rates, reset dates, grace periods, term extensions, monthly-payment changes, and conditions for retaining preferential rates.
5. Lower Monthly Payments Can Mean More Total Interest
Compare the same KRW 100M balance with level monthly principal-and-interest payments. A has 120 months remaining at 5% a year; B starts a new 180-month term at 4%. Both rates stay fixed, there is no grace period, and fees and early repayments are excluded. These are illustrative inputs, not lender quotes.
| Metric | Baseline A | Current B |
|---|---|---|
| Annual rate | 5% | 4% |
| Term | 120 months | 180 months |
| Monthly payment | KRW 1,060,655 | KRW 739,688 |
| Total interest | KRW 27,278,618 | KRW 33,143,827 |
| Total principal + interest | KRW 127,278,618 | KRW 133,143,827 |
Using the displayed values, B cuts the monthly payment by KRW 320,967 but adds KRW 5,865,209 in total interest across 60 extra months. Easing monthly cash flow is different from reducing total cost. Totals sum unrounded installments before rounding, so multiplying the displayed monthly payment by the term can give a slightly different amount.
Reproduce the example in the calculator
- Open loan scenario A/B comparison and select the month unit for the loan period. Enter KRW 100M, 5%, 120 months, no grace period, and equal-payment repayment.
- Pin the current scenario as baseline A, then change the rate to 4% and the term to 180 months.
- Check both monthly payments and total interest. Set B to 120 months too if you want to isolate the rate change.
For a real refinance, enter the current balance and remaining term for A, not the original loan term. Financing fees can also change the new principal. This table is not a refinancing profit calculation or recommendation: lender-specific daily interest, floating rates and cost quotes require separate review.
Page 2 of the CFPB refinancing handout explains this term-and-total-cost tradeoff. It supports the general repayment principle, not Korean fee rules or a particular lender's offer.
6. Include Payoff and New-Loan Costs
The refinancing comparison including fees shows payments, interest, and entered costs for keeping the existing loan versus switching. Enter thecurrent balance and remaining months, rather than the amount and full term at origination. Enter separate lender quotes for the early-repayment fee and new-loan costs you pay. If a cost is unknown, obtain a quote for your planned payoff date before treating it as zero.
The FSC's 2025 early-repayment-fee reform Q&A distinguishes contract and renewal dates, an exception for renewals with unchanged key terms, and annual rate disclosures. A single fee percentage cannot determine every loan's charge. The iM Bank loan disclosure also separates customer-paid and bank-paid costs. Include only your actual share in new-loan costs; the disclosure's illustrative rates and amounts are not your current quote.
Same Balance and Term, Two Ways to Pay the Fees
Assume a KRW 100M balance, 5% on the old loan and 4% on the new loan, both for 120 months with no grace period and equal principal-and-interest payments. A KRW 1M early-repayment fee and KRW 200K customer-paid new-loan costs are illustrative inputs, not a lender's quote. Both refinancing options use the same KRW 1.2M costs.
| Metric | Keep existing | Pay fees upfront | Finance fees |
|---|---|---|---|
| Loan principal to repay | KRW 100,000,000 | KRW 100,000,000 | KRW 101,200,000 |
| Separate upfront costs | KRW 0 | KRW 1,200,000 | KRW 0 |
| First monthly payment | KRW 1,060,655 | KRW 1,012,451 | KRW 1,024,601 |
| Remaining total interest | KRW 27,278,618 | KRW 21,494,166 | KRW 21,752,096 |
| Nominal payments plus costs | KRW 127,278,618 | KRW 122,694,166 | KRW 122,952,096 |
Paying the KRW 1.2M costs upfront reduces nominal payments plus costs by KRW 4,584,452 versus keeping the old loan. Financing them increases the new principal to KRW 101.2M and adds interest on those costs, leaving a reduction of KRW 4,326,522. The financed KRW 1.2M is not added a second time as an upfront cost. Whether you can borrow it depends on the lender's limit and approval.
Estimated switching-cost recovery is month 15 with upfront payment and month 16 with financing. This is the first month when cumulative interest differences cover the costs and continue to cover them through both maturities. It is not the settlement profit from selling or repaying early in that month.
- In the fee comparison, enter the existing KRW 100M balance, 5% annual rate, 120 months remaining, zero grace months, and equal-payment repayment.
- Set the new loan to 4%, 120 months, zero grace months, and equal payments. Enter the KRW 1M early-repayment fee and KRW 200K new-loan costs.
- Switch between paying fees upfront and financing them, checking both the first monthly payment and the nominal total-cost difference.
Results assume constant entered rates and sum principal, interest, and entered costs toeach loan's own maturity. Different terms do not share an end date, and future amounts are not discounted to present value. Cost recovery is not fees divided by the monthly payment difference, and it is not a refinancing recommendation. Daily payoff interest, floating-rate resets, additional early repayments, recurring guarantee or insurance premiums, tax deductions, and fee refunds are excluded. Interest is summed before whole-KRW rounding, then principal and costs are added. Totals can differ from the displayed monthly payment multiplied by the term.
7. Tools to Check Against Actual Schedules
These tools do not produce a complete refinancing recommendation; compare their schedules with lender payoff statements and fee quotes.
- Loan-refinancing infrastructure and cost disclosure — Financial Services Commission
- Bank of Korea base-rate history — Bank of Korea
⚠️ Disclaimer — This article is reference information compiled from published statutes, official notices and public agency data. It is not legal, tax or investment advice. Rules and rates change frequently and outcomes depend on your individual circumstances — always verify with the relevant authority, your financial institution, or a professional before acting. Worked examples are illustrative and may differ from actual amounts.