What This Calculator Does
A mortgage refinance involves replacing your existing loan with a new one — ideally at a lower interest rate. But refinancing always has a cost: closing fees typically run 2–5% of the loan amount, or $4,000–$10,000 on a $300,000 loan. The core questions every refinance decision requires answering are: How many months until my accumulated monthly savings cover those closing costs? And more importantly: Given how long I actually plan to stay in this home, will I come out ahead?
This calculator goes beyond a plain mortgage calculator by modeling both the break-even point (when savings offset costs) and the stay-horizon net savings — the actual dollars you pocket if you stay for your specified number of years. The distinction matters because lifetime interest savings can be misleading: resetting from a 27-year remaining term to a new 30-year loan looks attractive on a per-month basis but adds years of compounding interest that can make the refinance net-negative over a lifetime even if you save money monthly.
Use this tool before calling your lender, before locking a rate, and again every time rates drop significantly. Bookmark your results and revisit when market rates move.
How Break-Even Is Computed
The break-even calculation is straightforward: divide your upfront closing costs by the monthly payment reduction. If closing costs are $5,500 and your new payment is $242 lower than your current payment, break-even = ⌈$5,500 ÷ $242⌉ = 23 months. You recover the investment at month 23.
But break-even alone is incomplete. Someone who plans to sell in 18 months has a clear answer: don't refinance. Someone staying 20 years also has a clear answer: absolutely refinance. The ambiguity lives in the 3–8 year range — and that's where the stay-horizon net savings number is most useful. It computes total payments under each scenario over exactly the years you plan to stay, making the comparison apples-to-apples.
A subtlety worth noting: lower rate ≠ savings if the term resets. Dropping from 6.75% with 27 years left to 5.5% over a new 30-year loan stretches your debt by 3 years. On a 10-year horizon you may save money monthly, but on a lifetime basis you end up paying more interest because you extended the amortization window. The calculator surfaces this "lifetime interest savings" figure with a clear sign — negative means the term reset hurt you in the long run, even if you got a lower rate.
Worked Numeric Example
A homeowner has a $280,000 balance at 6.75% with 27 years remaining. Their monthly principal + interest is approximately $1,832. A refinance offer: 5.50% over 30 years, $5,500 closing costs paid upfront.
New monthly P&I ≈ $1,590. Monthly savings = $1,832 − $1,590 = $242. Break-even = ⌈$5,500 ÷ $242⌉ = 23 months. If the homeowner stays 10 years, they save 120 × $242 = $29,040 in payments minus $5,500 closing costs = $23,540 net savings on a 10-year horizon.
However, lifetime interest tells a different story. The original loan had 27 years remaining — the new loan resets to 30. Compounding over the extra 3 years, total lifetime interest rises by roughly $46,000, even at the lower rate. This illustrates why stay-horizon net savings, not lifetime interest, should drive your decision — unless you genuinely plan to keep the loan for its entire term.
Frequently Asked Questions
Should I roll closing costs into the loan?
Rolling closing costs into the loan eliminates the upfront payment but increases your principal, meaning you pay interest on those costs for the life of the loan. For a $5,500 roll-in at 5.5% over 30 years, you pay about $5,800 extra in interest — roughly doubling the effective cost. Pay upfront if you have the cash and plan to stay past break-even.
Does a "no-closing-cost" refinance ever beat paying upfront?
A no-closing-cost refi trades a slightly higher interest rate (typically +0.125–0.25%) for zero upfront fees. If you plan to sell or refinance again within 3–5 years, the higher rate usually costs less than paying $5,000–$8,000 upfront. If you plan to stay 10+ years, paying upfront wins almost every time. Use this calculator to compare scenarios directly.
How does a cash-out refinance change break-even?
Cash-out increases your new loan balance, raising your new monthly payment and eroding the monthly savings. It can push break-even past your planned stay horizon. However, if you use the cash to eliminate higher-rate debt (e.g., credit cards at 20%+), the combined savings may still make it worthwhile. Model each scenario separately.
What rate drop justifies a refinance?
The old "need at least 1%" rule is outdated. What matters is: (monthly savings) × (months you stay) > closing costs. On a $300k loan, dropping from 7% to 6.5% saves about $100/month. With $6,000 in closing costs, break-even is 60 months — fine if you plan to stay 7+ years, bad if you plan to sell in 4. There is no universal rate-drop threshold; run your specific numbers.