Business and Financial Tools
Mortgage Refinance Comparison Calculator
Compare interest, monthly payments, remaining principal and switching-cost recovery over your chosen period.
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Mortgage Refinance Comparison
Adjust assumptions and calculate. Your inputs stay in the browser.
From your assumptions
Calculation results
Net savings compare cumulative interest minus switching costs over the chosen period; this is not an investment return or NPV.
View the monthly comparison
| Month | Old payment | New payment | Old balance | New balance | Cumulative net interest savings |
|---|
Monthly reducing-balance simulation using annual rate ÷ 12. Annuity payments round to satang and the final installment closes the balance. Old rate is constant; new rates have a user-defined promotional and later phase. Switching costs are paid separately. Excludes daily accrual, floating-rate forecasts, approval, taxes and present-value discounting. Cost recovery means the first crossing within the chosen period; savings may turn negative again later.
Quick answer
When does refinancing a mortgage recover its switching costs?
Compare cumulative old interest minus new interest minus upfront switching costs over the same period. A lower monthly payment can come from a longer term, so compare remaining principal too. The calculator separates cash-flow relief from net interest savings.
How to use this tool
- Enter outstanding principal, assumed old rate and remaining term.
- Enter new term, promotional rate and length, and assumed later rate. Set promotion to 0 to start at the later rate.
- Enter incremental registration, appraisal, penalty/clawback, insurance and other costs, paid outside the new loan.
- Choose a comparison period. Review net interest savings and remaining principal together.
- Inspect monthly details and export Print, Excel, PDF or TXT.
How the calculation works
Monthly annuity payment = P×r÷[1−(1+r)^−n], with r equal to nominal annual rate divided by 12; at zero interest use P÷n. Payments round to satang. Each month rounds interest on opening principal, subtracts principal repaid and closes the final balance at maturity. The old rate is constant. The new loan changes rate after the promotion and re-amortizes the remaining balance over the remaining term. Net interest savings equal old interest minus new interest minus separately paid switching costs.
Examples
| Example | Input | Expected result |
|---|---|---|
| 3% promotion versus 6% over 36 months | |
Old payment THB 14,328.62; initial new payment 11,091.95; net interest savings 155,431.65; first recovery in month 5. |
| Manually check two months | |
Old payment THB 106.62; new 100; old interest 23.05; net savings THB 13.05. |
| Identical loan assumptions | |
No interest saved; net savings −THB 20,000; no recovery within the period. |
Limitations
- Monthly nominal-rate/12 model, not contractual daily accrual. Actual schedules can differ due to payment dates and rounding.
- Old rate stays constant; new loan supports one promotional and one later rate. No MRR/MLR forecast or multiple yearly rate steps.
- Excludes additional borrowing, financed fees, prepayments, insurance refunds, tax and NPV. Enter incremental net costs appropriate to your case.
- Principal accepts THB 0.01–100,000,000; rates 0–30% yearly, up to two decimals; terms and horizon 1–600 whole months; promotion 0–600. Annuity estimation uses floating-point math rounded to satang; ledger arithmetic uses integer satang.
- First cost recovery is only the first crossing within the horizon and can reverse later. This is not a savings or approval guarantee.
Frequently asked questions
Does a lower payment mean refinancing is cheaper?
A longer term can lower payments while repaying principal more slowly. Compare interest, switching costs and remaining balances. Cash-flow difference is separate from net interest savings.
Does first cost recovery guarantee lasting savings?
No. It is the first crossing in the selected period. Savings may later turn negative after promotion expiry, so review the final net amount too.
What does a zero promotion term mean?
The later-rate input becomes the initial rate and stays constant under the model. The promotional-rate input is unused.
Which switching costs belong here?
Include incremental registration, appraisal, penalty/clawback, insurance and other costs from your actual agreement. They are paid separately and not financed into the new principal.
Is this a bank quotation?
It is a monthly scenario based on entered rates. It does not fetch floating rates, decide approval or calculate an official payoff amount.
References
- ธปท. — เปรียบเทียบรีไฟแนนซ์และรีเทนชัน / Refinance and retention Verified 2026-10-06
- ธปท. — ดอกเบี้ยลดต้นลดดอก / Reducing-balance interest Verified 2026-10-06
- Microsoft — สูตรเงินงวด PMT / Monthly annuity payment Verified 2026-10-06
Content and calculation method last reviewed: