About that 3% rate.
Bought 2018–2021? Let's run the actual numbers.
Let's start with the objection
You may never see
that rate again.
There. We said it first. Keeping a 3% mortgage feels like the only rational move — and sometimes it genuinely is. This page is about how to know whether you're in the exception.
If you bought between 2018 and 2021, you're probably holding two things at once: a mortgage rate that looks like a typo today, and a home that no longer quite fits — too small since the household grew, too big since it shrank, too far from where life moved. So you stay. Economists call it the rate lock-in effect, and it's measurably real: federal researchers found that every percentage point between your rate and today's market cuts the odds you'll sell in a given quarter by about 18% (FHFA Working Paper 24-03, 2024). You're also in enormous company — as of Q1 2026, 49.9% of U.S. mortgages still carry rates under 4%, and roughly one in five sits under 3% (FHFA National Mortgage Database).
But here's what the monthly-payment comparison hides: the rate is only one line of the ledger. On the other lines sit the equity your home has built since you bought it, what that equity does to the size of the next loan, and what staying put quietly costs — the commute, the renovation you keep pricing, the second bathroom that doesn't exist. It may even matter less than it feels: when Redfin surveyed owners in November 2025 about why they're staying put, only 16% named their mortgage rate. Nobody can tell you the answer without your numbers. What we can do is show you the shape of the math.
The shape of the math
An illustration —
not a quote.
Hypothetical household, round numbers, clearly labeled. Your situation will differ — that's exactly why we run it person by person.
Say a household bought a Greater Boston home in 2019 for $550,000 with 20% down at 3.1%. Two things have been happening since, and only one of them shows up on the mortgage statement:
The loan shrank while the home grew. Six-plus years of payments have cut the balance well below $400,000 — while area values have climbed enough that a home like that may be worth several hundred thousand dollars more than it cost. Add those together and the household's equity is likely north of half a million dollars. The 3% rate applies to the shrinking number, not the growing one.
Equity rolled forward changes the next loan entirely. Move that equity into the next purchase and the new mortgage — whatever the rate — applies to a far smaller balance. A higher rate on a much smaller loan can land closer to the old payment than the rate alone suggests, especially for anyone right-sizing rather than upsizing. And that's before asking what the extra bedroom, the shorter commute, or the single floor is worth per month in real life.
Sometimes the answer really is "keep the rate." When the math says stay, we'll say stay — or show you the third option below that most people never price. If you want to understand the mechanics first, start with our explainers on what a mortgage and note actually are and reading a loan estimate.
Market data last reviewed July 2026 · Sources: FHFA National Mortgage Database (Q1 2026) · FHFA Working Paper 24-03 (2024) · Redfin homeowner survey (Nov 2025). Historical figures only — we don't publish rate forecasts, and any payment-specific numbers for your situation come from a licensed mortgage professional.
Four reframes
What the payment comparison
doesn't show.
The lock-in framing treats the rate as the whole decision. It's one input among four.
You Keep the Rate, Not the Spread
The rate saves you a known amount each month. The equity spread — what your home gained versus what the right next home costs — is often the bigger number, and it only becomes real when you act on it.
Staying Has a Price Tag Too
The renovation to make the house work, the commute in hours per week, the space you rent by heating it. "Do nothing" is also a financial decision — it just never sends a bill with a total on it.
Rolled Equity Shrinks the New Loan
The rate applies to the balance, and the balance is what your equity determines. Households sitting on large gains often need a far smaller mortgage than they had in 2019 — which is how a bigger rate can meet a similar payment.
Or: Keep the Rate AND Move
The option almost nobody prices: keep the low-rate home as a rental, let tenants carry the mortgage, and buy the next place. It isn't for everyone — but our rental practice can tell you what your home would lease for, which is the number that decides it.
Line one of the ledger
Start with what
the house is worth.
Every version of this math starts from the same number: what your home is worth today. Type the address and see the estimate right here — then we can talk about what to do with it, or not.
Automated estimate — a starting point, not an appraisal or a formal market analysis. Provided with our lending partner. For what the number means on your specific house, ask us for the human version.
Who runs the numbers
Blake Sherwood
Vice President · Team Lead
Blake has walked hundreds of Greater Boston households through exactly this decision — including plenty he advised to stay put. The analysis covers what your home nets today, what the realistic next-home budget looks like, how the sequence works so you're never homeless in between, and what the rental option would earn instead. Numbers first, opinions second, your call always.
617.833.0036 · blake.sherwood@compass.com
Get My Numbers“A 3% rate is a great reason not to move badly. It's a terrible reason not to do the math.” Blake Sherwood · Sherwood & Company
Not ready to talk? Start with the guide.
Stay / Sell / Rent-It-Out Worksheet
The three-path math from this page as a fill-in worksheet — your equity, your next-loan size, what the house would rent for — refreshed quarterly as the market data updates.
Get in touch
Run your numbers
Start with the address. We'll put together the actual math for your situation — sell, stay, or rent it out — with no pressure and no obligation to act on any of it.