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Finance & LoansGenerated accuracy model review: 2026-05-06
Refinance Calculator accuracy and testing
This page documents how Calwarden builds trust for this calculator: source notes, regression-style default tests, limitations, assumptions, unit handling, rounding, and visible change history.
Formula source
- The tool calculates the monthly payment for both the old and new loan scenarios. **Break-Even Point (Months)** = Closing Costs / Monthly Savings. If you plan to stay in the home longer than the break-even period, refinancing usually makes sense.
Test cases
Default input regression check
Generated from the checked-in default inputs and calculate function.
Inputs
- Loan Balance: $200,000
- Current Rate: 6.5%
- New Rate: 5.5%
- Loan Term: 30 Years
- Closing Costs: $4,000
Expected outputs
- Monthly Savings: $128.56
- Break-Even Time: 32 months
- Lifetime Savings: $42,280.90
Known limitations
- Assumes you keep the loan for its full term for lifetime savings calculation. Does not account for investing the monthly savings.
Assumptions
- The current and new loans are modeled over the same term for a simple apples-to-apples payment comparison.
- Closing costs are paid upfront and recovered only through monthly payment savings.
- Lifetime savings assumes you keep the refinanced loan long enough for the modeled savings to occur.
Unit handling
- Loan Balance accepts values in $.
- Current Rate accepts values in %.
- New Rate accepts values in %.
- Loan Term accepts values in Years.
- Closing Costs accepts values in $.
- Monthly Savings is displayed as currency.
- Lifetime Savings is displayed as currency.
Rounding rules
- Number displays use up to 2 decimal places in the calculator UI.
- Currency outputs are displayed with standard US dollar formatting.
Version history
1.0.0 - 2026-05-06
Generated accuracy and testing page from the current refinance-calculator calculator definition.
Change log
2026-05-06
Published default regression test documentation and metadata fallbacks for Refinance Calculator.
Calculator transparency
Accuracy pages are generated from checked-in calculator definitions and can be upgraded with curated review metadata over time.