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Mortgage Refinance Calculator

How It Works

Mortgage refinancing replaces your existing home loan with a new one — typically to secure a lower interest rate, reduce your monthly payment, shorten your loan term, or access home equity. The central question is always the same: will the long-term savings outweigh the upfront costs, and how long will it take to break even?

The break-even point is the number of months it takes for your monthly savings to recover the closing costs you paid to refinance. If your new loan saves you $300/month and refinancing cost $6,000, your break-even is 20 months. If you plan to stay in the home beyond that point, refinancing makes financial sense. If you expect to move within 20 months, the costs won't be recovered.

Closing costs on a refinance typically range from 2% to 5% of the loan amount, covering lender origination fees, appraisal, title insurance, and government recording fees. Some lenders offer "no-closing-cost" refinances — but these costs are either rolled into the loan balance or recouped through a slightly higher interest rate. Nothing is truly free.

The common "1% rule" — that refinancing is worthwhile when you can lower your rate by at least 1% — is a rough heuristic, not a financial law. A 0.75% rate drop on a large loan balance can generate significant monthly savings and a short break-even period. Conversely, refinancing for a 1.5% rate reduction on a small remaining balance may not justify the closing costs.

One often-overlooked consideration is loan term extension. Refinancing a 25-year remaining loan into a new 30-year loan lowers your monthly payment but extends debt repayment by 5 years and can increase total interest paid even at a lower rate. This calculator shows both monthly savings and total interest paid so you can evaluate the complete trade-off.

Cash-out refinancing — where you borrow more than your current balance to access equity — is a different calculation entirely. This calculator focuses on rate-and-term refinancing, where the goal is to lower your rate or change your loan term without increasing your loan balance.

To qualify for the best refinance rates, lenders typically require a credit score above 740, equity of at least 20%, stable income, and a debt-to-income ratio below 43%. Rates advertised in the media are often for ideal borrowers; your actual offer may differ.

Formula Breakdown

MONTHLY PAYMENT (both current and new):
  M = P[r(1+r)^n] / [(1+r)^n − 1]
  Where P = loan balance, r = monthly rate (annual rate / 12), n = months remaining

MONTHLY SAVINGS:
  Monthly Savings = Current Monthly Payment − New Monthly Payment

BREAK-EVEN MONTHS:
  Break-Even = ceil(Closing Costs / Monthly Savings)
  If Monthly Savings ≤ 0: Break-Even = "Never"

TOTAL INTEREST:
  Total Interest = (Monthly Payment × Total Months) − Principal

INTEREST SAVINGS:
  Interest Savings = Current Total Interest − New Total Interest − Closing Costs
  (Can be negative if new term is significantly longer)

TOTAL COST COMPARISON:
  Current Total Cost = Current Payment × Remaining Months
  New Total Cost = (New Payment × New Term Months) + Closing Costs

EXAMPLE (defaults: $380k balance, 7.5% → 6.0%, 25yr → 30yr, $6k closing):
  Current payment: ~$2,802/month on $380k at 7.5% for 25 years
  New payment: ~$2,278/month on $380k at 6.0% for 30 years
  Monthly savings: ~$524
  Break-even: ceil($6,000 / $524) = 12 months
  Total interest (current): ~$460,600 over remaining 25 years
  Total interest (new): ~$440,000 over 30 years
  Note: longer term partially offsets lower rate benefit

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