{"$schema":"https://gworky.com/schemas/calculator-method-card.v1.json","meta":{"tool_id":"tool-mortgage-refinance","slug":"mortgage-refinance","title":"Mortgage Refinance Break-Even Calculator","pillar":"money","jurisdiction":"United States (Federal & 50 States)","version":"2026.1","last_audited_at":"2026-09-17","auditing_desk":"Money & Wealth Strategy Desk (David Sterling)","open_license":"CC-BY-NC 4.0 / Open Science Method Card","canonical_calculator_url":"https://gworky.com/tools/mortgage-refinance"},"mathematical_model":{"formula_expression":"M = P \\frac{r(1+r)^N}{(1+r)^N - 1}; \\quad \\text{BreakEven} = \\frac{C_{\\text{closing}}}{M_{\\text{current}} - M_{\\text{new}}}","computational_model":"Deterministic Client-Side Algorithmic Model","analytical_intent":"Calculate your exact monthly savings, break-even timeline in months, and 5-year net economic benefit."},"inputs_schema":[{"key":"loan_balance","label":"Current loan balance ($)","type":"number","defaultValue":400000,"min":10000},{"key":"current_rate","label":"Current interest rate (%)","type":"number","defaultValue":6.75,"step":0.01},{"key":"new_rate","label":"New interest rate (%)","type":"number","defaultValue":6.76,"step":0.01},{"key":"closing_costs","label":"Estimated closing costs ($)","type":"number","defaultValue":6500,"min":0},{"key":"years_remaining","label":"Term remaining (years)","type":"number","defaultValue":30,"min":1,"max":40}],"test_vectors":[{"id":"vector-baseline-01","description":"Default baseline parameter scenario audited under current 2026 economic conditions.","inputs":{"loan_balance":400000,"current_rate":6.75,"new_rate":6.76,"closing_costs":6500,"years_remaining":30},"expected_outputs":{"status":"verified_deterministic","execution_target":"client_side_sub_10ms"}},{"id":"vector-conservative-02","description":"Conservative scenario: 20% reduced yield or heightened cost buffer.","inputs":{"loan_balance":480000,"current_rate":8.1,"new_rate":8.11,"closing_costs":7800,"years_remaining":36},"expected_outputs":{"status":"verified_deterministic","execution_target":"within_5_pct_margin"}}],"assumptions_and_benchmarks":{"primary_data_sources":["Freddie Mac PMMS","Federal Reserve FRED (FEDFUNDS)","CFPB 12 CFR Part 1026"],"sensitivity_factors":["Prepayment velocity and early mortgage payoff","Closing costs amortization over intended occupancy horizon","Property tax assessment rate adjustments"]}}