How your existing mortgage rate changes the renovate-vs-move decision
A low mortgage rate is an asset you cannot take with you. This guide puts a dollar figure on what giving it up costs over the years you would actually stay, explains why comparing monthly payments understates it, and shows the cases where moving still comes out ahead.
By Hearthfork Research · · Methodology
Key takeaways
- About half of U.S. mortgages carry a rate under 4% and roughly two thirds are under 5% (FHFA National Mortgage Database, Q1 2026), against a 30-year average of 6.67% in August 2026.
- Giving up a rate shows up in three places: a higher payment, more cumulative interest, and a larger balance left at the end. In the worked example, a 2.75% to 6.75% swap on a $720,000 loan costs about $1,700 a month and roughly $356,000 over ten years.
- Comparing payments alone is wrong in both directions: it ignores principal, which builds equity, and it ignores the slower amortization and compounding of the cash you pay out.
- Moving can still win with a low rate when you are downsizing, when the new loan is small, when the renovation you would otherwise do is very large, or when your current rate is not far below the market.
The direct answer
If your mortgage rate is two or more points below what you would pay on a new loan, and the new loan would be as large or larger than your current balance, the cost of giving up your rate is usually the single largest number in the renovate-versus-move comparison, bigger than the commission and often bigger than the entire renovation. It is not, however, a reason to stay regardless. The cost is proportional to the size of the new loan and the number of years you keep it, so a smaller loan, a shorter stay, or a current rate already near the market shrinks it to something a move can overcome.
How common lock-in is
The Federal Housing Finance Agency’s National Mortgage Database for the first quarter of 2026, as summarized by Calculated Risk and Wolf Street on July 1, 2026, shows that 19.5% of outstanding mortgages carried a rate under 3%, 49.9% were under 4%, 66.7% under 5%, and 77.9% under 6%; only 22.1% were at 6% or above. Redfin’s analysis of the second quarter of 2025, reported by National Mortgage Professional on September 29, 2025, put the comparable figures at 20.4% under 3%, 52.5% under 4% and 70.4% under 5%. Freddie Mac’s Primary Mortgage Market Survey reported a 30-year fixed average of 6.67% on August 13, 2026.
The behavioral effect is well documented. The New York Fed’s Liberty Street Economics blog (May 6, 2024) estimated that each one-point reduction in the gap between a household’s rate and the market rate raises the probability of moving within three years by about 3.5 percentage points. Freddie Mac estimated in July 2023 that the average locked-in household held roughly $55,000 of value in its below-market rate, using an example of $493 a month saved at 2.65% versus 6.81%. Lock-in is easing as rates drift and life events accumulate: Coldwell Banker’s April 2026 Home Shopping Season report found 35% of sellers with sub-5% rates listing anyway, though 61% of agents still described lock-in as a major or moderate factor. Surveys by Redfin and Ipsos (reported April 23, 2026) found 65% of recent and 71% of planned home-improvement projects were chosen instead of relocating, and a Citizens survey the same month found 19% of homeowners citing their mortgage rate as the reason renovation was their most realistic option.
The three places a given-up rate costs you
When you sell and buy, you replace one loan with another. Suppose the new loan is $720,000 over thirty years, as in the worked example. At 6.75% the principal-and-interest payment is about $4,700 a month; if you could somehow carry your 2.75% rate onto that balance it would be about $2,900. The difference, $1,700 a month, is the first and most visible cost.
The second is cumulative interest. Over ten years the 6.75% loan accrues roughly $280,000 more interest than the same balance at 2.75%. The third is the remaining balance: because a higher-rate loan devotes more of each payment to interest, less goes to principal, and after ten years you owe about $72,000 more than you would have at the lower rate. That difference is equity you do not have.
The calculator reports all three, then a fourth figure that combines them properly: the total effect, which is the change in the renovate-versus-move result when the move path is re-run with the new mortgage priced at your existing rate and nothing else changed. In the worked example it is approximately $356,000 over ten years. That is larger than the payment difference multiplied by 120 months ($208,000), because the extra cash you pay out each month is also cash that could have been earning a return, and the model compounds it at the rate you assume on retained capital.
Why comparing payments alone is wrong
A common shortcut is to compare the old payment with the new payment and call the difference the cost of moving. It fails in two ways. First, a payment is not a cost. Part of it is principal, which reduces what you owe and stays with you as equity; only the interest is gone. A household moving from a $1,400 payment on a 2.75% loan to a $4,700 payment on a 6.75% loan is not $3,300 a month poorer, because more than $600 of the new payment is principal. Second, payments ignore what happens to the balance. Two loans with the same payment but different rates leave you owing very different amounts after ten years. The right comparison is the one the engine makes: interest as a cost, principal as a transfer into equity, the remaining balance at the horizon, and the opportunity cost of the cash that left the household along the way. The methodology sets out the exact formulas.
A worked example
The household below has a $550,000 home with a $300,000 balance at 2.75% and 25 years remaining. It is weighing a $150,000 renovation against a $900,000 home financed with $180,000 down at 6.75%. Every number is produced by the calculator’s engine from those inputs.
The rate gap accounts for roughly $356,000 of the $357,000 gap, which is essentially all of it; the result survives every sensitivity test.
| Inputs | |
|---|---|
| Current home value | $550,000 |
| Mortgage balance / rate | $300,000 at 2.75% |
| Renovation cost + 15% contingency | $150,000 → $172,500 |
| Soft costs (design, permits, temporary housing) | $14,000 |
| Value recouped | 60% → $103,500 added |
| Renovation funding | 50% cash, rest financed at 8.31% |
| Replacement home price | $900,000 |
| New mortgage | $720,000 at 6.75% |
| Selling costs (commission, closing, pre-listing) | $44,600 |
| Buying costs (closing, moving, setup) | $30,000 |
| Horizon / appreciation / return on cash | 10 yrs / 3.5% / 6.0% |
| Results after 10 years (approximate) | |
|---|---|
| Cash needed at the start (renovate / move) | $100,000 / $4,600 |
| Monthly housing outlay, month 1 (renovate / move) | $3,400 / $6,600 |
| Interest paid over horizon (renovate / move) | $126,000 / $455,000 |
| Home equity at horizon (renovate / move) | $673,000 / $655,000 |
| Opportunity credit to the cheaper path | Renovate +$338,000 |
| Financial position (renovate / move) | $1,010,000 / $655,000 |
| Cost of giving up the 2.75% rate | $1,700/mo more; $356,000 total effect |
| Maximum renovation budget (before contingency) | $391,000 |
| Replacement-price break-even | $521,000 |
| New-rate break-even | 2.74% |
| Time break-even | Lead never reverses within 30 years |
| Stability | Strong result |
Two outputs are worth dwelling on. The new-rate break-even says moving would pull ahead only if the new home could be financed at about 2.74% or lower, which is to say at roughly the household’s current rate. And the maximum renovation budget of about $391,000 says this household could spend well over twice its planned amount before moving became the better financial choice. Both are consequences of the same fact: the move path is carrying $720,000 of debt at a rate four points higher than the renovate path’s $300,000.
When moving still wins despite a low rate
A low rate is a large asset, not an infinite one. The cost of giving it up scales with the new loan balance, the rate gap, and the years you keep the loan, and several common situations shrink one of those enough for moving to win.
Downsizing. If the replacement home is cheaper, the new loan may be small, and moving may free equity that goes to work elsewhere. In the calculator’s downsizing scenario (a 3.5% mortgage, a $120,000 renovation, a $400,000 replacement home at 6.67%), the rate gap is worth about $95,000 in renovating’s favor, yet moving still comes out roughly $107,000 ahead over ten years, because the move frees cash at the start and cuts monthly outlay.
A very large renovation. When the project costs a large share of the home’s value and recoups little, the unrecouped cost can exceed the rate advantage. In the calculator’s large-addition scenario (a 5.5% mortgage, a $400,000 addition recouping 40%, a $650,000 replacement home at 6.5%), the rate gap is worth about $57,500, and moving wins by roughly $653,000.
A rate already near the market. If your loan is at 5.5% and the market is at 6.5%, the gap is one point and the lock-in effect is correspondingly modest. A short stay. The interest and balance effects accumulate over time; over three years they are a fraction of what they are over fifteen. A location problem. If the reason for moving is schools, commute or neighborhood, the rate is the price of solving it, not a veto.
Keeping the rate while still changing homes
Some households look for ways to keep a low rate and move anyway. An assumable mortgage (common on FHA and VA loans) lets a buyer take over your rate, which can make your home more valuable to sell but does nothing for the loan you take out next. Renting out the current home and buying another keeps the rate but turns you into a landlord with a second mortgage at today’s rate. A recast lowers a payment but not the rate. A seller- or builder-paid buydown reduces the new rate temporarily. None of these is modeled by the calculator; each changes the question rather than answering it, and each deserves advice specific to your situation.
Financing a renovation without touching the first mortgage
The other half of the lock-in decision is how to pay for the renovation without refinancing the low-rate loan. A HELOC (national average 8.31% on August 20, 2026, per Fortune and Mortgage Research Center) or a home-equity loan (about 8.44% for a 15-year term on the same date) sits behind the first mortgage, so your blended cost of borrowing rises only on the new money. The calculator models the financed share as a second amortizing loan at the rate and term you enter; its interest is a cost and its balance reduces your equity until repaid. Even at 8% or 9%, borrowing $86,000 on a second lien is far cheaper than re-borrowing $720,000 at 6.75%, which is the comparison that actually matters.
How to put your own rate into the calculator
Enter your current balance, rate and remaining term from your most recent statement, then the price, down payment and quoted rate for the home you would buy. The lock-in panel in the results reports the monthly payment difference, additional interest over your horizon, the difference in remaining balance, and the total effect on the verdict. If the total effect is most of the gap between the two paths, your decision is essentially a decision about the rate, and the new-rate break-even tells you how far rates would have to fall before moving became competitive.
Educational estimates based on your assumptions. Not financial, mortgage, tax, legal, appraisal, construction or real-estate advice.