When to Refinance Your Mortgage: The Math and the Common Mistakes
Rate drops aren't the only reason to refinance — but they're the most common, and the math is unforgiving. Here's how to know if it's worth it for your loan.
The classic refinance: drop your rate
The headline reason: take your existing 7.25% mortgage and replace it with a new 6.25% mortgage on the same balance. Same loan amount, lower rate, lower payment.
On a $400,000 balance:
- 7.25% rate: $2,729/month P&I
- 6.25% rate: $2,463/month P&I
- Monthly savings: $266
- Annual savings: $3,192
Refinance closing costs typically run 2–5% of loan amount — $8,000–$20,000 on a $400k loan. Divide closing costs by monthly savings to find breakeven time:
- $10,000 closing cost ÷ $266 = 38 months to break even
If you'll stay in the home longer than 38 months, the refinance wins. If you'll sell or refi again sooner, it loses.
The 1% rule (outdated) vs the actual rule
The old rule: "Only refinance if you can drop your rate by at least 1%."
Modern rule: Refinance if breakeven is less than half your expected remaining holding period. A 0.5% drop on a large loan, with low closing costs, can pencil out perfectly.
When refinancing makes sense
Lower rate (the obvious one)
If current market rates are at least 0.5% below your current rate AND you'll stay long enough to recoup closing costs, refinance.
Drop PMI
If you put less than 20% down on an FHA loan, you're paying MIP for life. Refinancing to conventional once you have 20% equity ends the insurance entirely. Even if rates are the same, eliminating $200/month in MIP is a strong win.
Shorten the term
Refinancing from a 30-year fixed to a 15-year fixed at any time saves enormous total interest. On a $300k balance:
- 30-year at 6.5%: $1,896/month, $382,633 total interest
- 15-year at 5.75%: $2,491/month, $148,332 total interest
You'll save $234,000 over the life of the loan. Worth it if you can afford the payment bump.
Cash-out refinance
Refinance your existing mortgage for more than you currently owe and take the difference in cash. Useful for:
- Major home renovations
- Consolidating high-interest debt
- Buying an investment property
Two big cautions:
- You're trading mortgage debt (cheap, deductible) for whatever you spend on (often not deductible). Be sure the use of funds justifies the new debt.
- You may be trading a low rate for a higher one. A homeowner with a 3% pandemic-era mortgage should never cash-out refi at 7% — use a HELOC instead.
Move from ARM to fixed (or vice versa)
Locking in a fixed rate when your ARM is about to start adjusting upward is often worthwhile, even at a higher rate, for the peace of mind.
Remove a co-borrower
After divorce, refinancing into one borrower's name only removes the other from the loan and the title. The remaining borrower must qualify alone for the new loan.
When refinancing doesn't make sense
- You're moving in less than 2 years
- The rate drop is under 0.5% and closing costs are high
- You'd extend the term back to 30 years (resetting amortization)
- You'd pull cash out for non-essential spending
- Your current rate is far below market (don't touch a 3% loan)
The reset-the-clock trap
Refinancing into another 30-year loan restarts your amortization schedule. A homeowner with 22 years left on a 30-year mortgage who refinances into a fresh 30-year loan now has 30 years of payments again, even if the monthly payment is lower.
Result: more total interest paid even at a lower rate.
The fix: when you refinance to a lower rate, keep your monthly payment the same (apply the difference as extra principal) OR refinance into a shorter term (20-year, 15-year). This captures the rate savings without extending the timeline.
Closing costs to expect
Similar to a purchase mortgage but typically lower because no title transfer or transfer taxes:
| Cost | Range |
|---|---|
| Origination / lender fees | $1,500–$5,000 |
| Appraisal | $500–$800 |
| Title (refinance policy) | $400–$1,200 |
| Recording fees | $100–$300 |
| Prepaid interest | Variable |
| Per-state mortgage tax | Variable (NY high) |
| Total typical | $3,000–$10,000 |
Plus reserves and escrow setup, which add another $2,000–$5,000.
Streamline refis: the easy path
If your existing loan is FHA, VA, or USDA, you may qualify for a "streamline" refinance with reduced underwriting:
- VA IRRRL (Interest Rate Reduction Refinance Loan): No appraisal usually, no income verification, much lower fees
- FHA Streamline: No appraisal in many cases, no income re-verification
- USDA Streamline: Similar reduced-doc process
These are dramatically cheaper than starting fresh and can be the difference between worthwhile and pointless on small rate drops.
How to shop a refinance
- Pull your current mortgage statement — note the rate, balance, monthly payment, term remaining.
- Get Loan Estimates from at least 3 lenders. Use a national bank, a local credit union, and an online lender (Better, Rocket, AmeriSave).
- Compare the Loan Estimates line-by-line. Focus on: interest rate, lender fees, origination charges, total closing costs.
- Calculate breakeven for each option.
- Watch for "lender credit" tradeoffs — slightly higher rate in exchange for lower upfront costs. Math the right one for your timeline.
How long the refi takes
- Application to closing: 30–60 days typical
- Streamline refi: 14–30 days
- Right of rescission: 3 business days after closing during which you can cancel a refinance on a primary residence (federal law)
The bottom line
The refinance math is unforgiving but simple. Calculate breakeven, compare against your holding horizon, and don't let "lower monthly payment" by itself tempt you into a worse deal. A 30-year mortgage you've already paid into for 5 years is a different beast than a fresh 30-year — handle accordingly.