Every mortgage calculator shows you principal and interest. Then the tax bill arrives, the roof ages, the insurance renews on a shoreline policy — and the real number turns out to be somewhere else entirely. This one shows the whole picture.
• CheapestOil · NewEnglandOil · HeatFleet — dealer prices by ZIP, updated daily
• EIA Connecticut survey — official, weekly Oct–Mar
• CT Office of Consumer Counsel — electric supply rates
Your own delivery ticket beats all of them.
How the maintenance number is figured
Most calculators either ignore maintenance or apply the old rule of thumb: one percent of the purchase price per year. That rule breaks badly in Connecticut, and it breaks in opposite directions depending on where you are.
Roofs, furnaces and siding are attached to the building. Land needs nothing. So on a Stonington waterfront parcel where more than half the price is the lot, one percent of price wildly overstates what the house will actually cost you to keep. In Hartford or Windham, where a home sells for close to what it would cost to rebuild, the same rule understates it.
This tool separates the two. It estimates what your house would cost to rebuild — its square footage times a rebuild cost per foot, adjusted for condition — treats the remainder of the price as land, and then sets a reserve against the building alone. Older houses reserve more, because more of their components are due. Coastal exposure raises it, because salt air is hard on everything it touches.
It’s an estimate, and an estimate is all it can be from a price and a town. If you enter your assessor’s own land and building values, it stops estimating and uses their split instead.
What updates itself here, and what doesn’t
Almost nothing. This tool runs entirely in your browser with no service behind it, so the interest rate, the fuel prices, and the electric rate are figures we typed in and periodically revise by hand. They were set in August 2026. Nothing reaches out for a live quote.
That matters most for the interest rate, which moves weekly. The default is the Freddie Mac national 30-year average, and it is a placeholder for arithmetic, not a rate anyone has offered you. Your credit, your down payment, your loan size and your lender will all move it. Put your actual quote in the box.
Energy defaults age on a known schedule. Connecticut electric supply rates reset every January and July, and heating fuel prices swing through the winter. If you have a bill or a delivery ticket, your own number is better than ours — every field is editable for exactly that reason.
The town data underneath — mill rates, median selling prices, median home sizes, revaluation years — is versioned deliberately and each result says which vintage it used.
What we left out, and why it’s yours to add
Snow removal, lawn care, water and sewer, septic, trash, internet — none of these are in the payment or the energy band, and they shouldn’t be assumed. Half the people reading this mow their own lawn and plow their own driveway. The other half write a cheque every month. So they sit in a third band you switch on line by line, with figures you can overwrite.
There is a structural reason they were missing. The maintenance reserve is calculated on the building, because roofs and furnaces belong to the house and not to the dirt. But mowing and plowing scale with the lot — the exact opposite. On a two-acre parcel those costs are real and the reserve never sees them.
Flood insurance starts at zero deliberately. A homeowners policy does not cover flood, ever, and on a coastal parcel a policy can run into four figures a year — and it is mandatory with a federally backed mortgage in a Special Flood Hazard Area. There is no honest default, so check the flood map for the address and get a quote.
Fire and special district taxes are the one that can distort the headline, and they are far more common than most buyers realise. Connecticut has 352 special taxing districts across 89 of its 169 towns — fire districts, boroughs, beach and shoreline associations, sewer and improvement districts — each levying on top of the town rate and billing separately. Stonington alone has eleven; Groton ten; Branford fourteen.
They also overlap, which is the part that catches people out. A parcel in the City of Groton can sit in the Groton Sewer District as well. Stonington Borough and the Stonington Fire District are separate levies on ground that overlaps. So the list here lets you tick more than one, and the rates add together the way the bills do.
Pick your town and the district list loads with its actual rates, taken from the state’s own mill rate file. Tick every one your parcel sits in and the tax line recalculates. Leave them all unticked in a town that has them and the result panel tells you the figure is understated rather than letting you assume the base rate is the whole story.
Check every number here yourself
Nothing on this page updates on its own, so here is where each assumption comes from and how fast it goes stale.
Interest rate — moves weekly.
Freddie Mac Primary Mortgage Market Survey, published Thursdays. Your lender’s quote beats the national average.
Heating oil and propane — moves daily, and dealer to dealer.
Compare live dealer prices by ZIP at CheapestOil, NewEnglandOil, or HeatFleet. For the official series, EIA’s Connecticut survey runs weekly from October through March and pauses for the summer, so an August figure there is always months stale.
The spread is worth the ten minutes. Connecticut dealer prices in late July 2026 ran from roughly $4.25 to $5.60 a gallon — on 800 gallons, that gap is over a thousand dollars a season for the identical fuel. Late summer is usually the cheapest window to lock in, before the heating season starts.
Electricity — supply rates reset every January and July.
CT Office of Consumer Counsel for rate alerts and supplier comparison. If your town has a municipal utility, use its published rate instead — the result panel links to it.
Mill rates and revaluation years — set each spring, effective July 1.
CT Office of Policy and Management publishes the statewide table, though individual towns adopt new rates months before OPM compiles them. The town assessor is always current.
Land and building values — change only at revaluation.
Vision assessor directory or, in southeastern Connecticut, the SECOG parcel viewer. These are the exact figures the tool would rather use than its own estimate.
Insurance and rebuild cost — no public source worth quoting.
Insurance is modeled here from structure value and water exposure. On the shoreline especially, wind deductibles and flood coverage move it enough that only a real quote means anything. Ask us and we’ll get you one.
Why energy sits in its own band
No lender underwrites your electric bill, so folding it into the payment would make this tool’s number impossible to compare against the quote your loan officer hands you. It sits below the payment instead, with its own subtotal and an all-in figure underneath.
It belongs on the page all the same. Connecticut carries some of the highest electricity rates in the country, and out here the older shoreline stock is mostly oil and propane. Heating fuel alone can differ by several thousand dollars a year between two houses of the same size on the same street — one on natural gas, one on propane.
The heating estimate works from the square footage and age of the house rather than a flat guess: an antique needs far more delivered heat per square foot than something built in the last decade. Then it converts that demand through the efficiency of whatever system you pick. Geothermal moves roughly four units of heat per unit of electricity, air-source about two and a half, and electric baseboard exactly one — which is why baseboard heat in Connecticut is punishing and why it belongs on the page before you buy, not after.
The municipal utility advantage nobody prices in
Most of Connecticut buys electricity from Eversource or United Illuminating. But seven municipal utilities serve pockets of the state — and four of them are in our backyard: Groton, Norwich, Bozrah, and the Jewett City borough of Griswold. Wallingford and two districts of Norwalk make up the rest.
They are not regulated by PURA; their rates are set by local commissions, and they consistently come in well under the investor-owned utilities. Reported savings run somewhere between a quarter and half the bill for a typical household.
That is a real, permanent, town-level cost difference that appears in no listing and no other calculator. It is also easy to get wrong: several of these utilities serve only part of a town. Jewett City’s utility covers the borough, not all of Griswold. Norwalk’s two districts cover South and East Norwalk. Always confirm the utility at the specific address — which is why we link to them rather than just naming them.
Where our tax figures come from
Mill rates are the official Connecticut Office of Policy and Management rates for FY 2025–2026, from the Grand List of October 1, 2024. That is the most recent complete statewide set OPM publishes.
Towns set their own rates each spring, so by mid-2026 some have moved on. Where we have confirmed a town’s adopted FY 2026–27 rate against the town’s own record, this tool uses it and says so. Where a rate has been proposed but not finally adopted, it says that too. And where a town has not published, we leave the older rate in place and tell you plainly that we did — rather than quietly showing you a number we can’t stand behind.
Every result panel names which basis it used. If your town shows anything other than a confirmed current rate, call the assessor before you rely on the figure.
Two things that break the 70% rule
Connecticut assesses homes at 70% of market value. Nearly everywhere. Two exceptions matter enough that this tool tracks them town by town.
Revaluation phase-ins. A town emerging from revaluation can spread the increase over several years rather than applying it at once. Assessments there are climbing toward 70% but haven’t arrived, so applying the full ratio overstates the tax. Milford and Norwalk are both phasing in.
Homestead exemptions. New Milford now assesses primary residences at 60% rather than 70%. Same house, same mill rate, materially different bill depending on whether you live there.
Where either applies, the panel above flags it and explains what the number does and doesn’t account for.
Information deemed reliable but not guaranteed. Every figure produced by this tool is an estimate built from public data and general assumptions. It is not an appraisal, a loan estimate, an insurance quote, or a tax determination, and no part of it creates a professional relationship or a representation of fact. Seaport Real Estate Services and Seaport Advisory make no warranty, express or implied, as to the accuracy or completeness of anything shown here, and accept no liability for any decision made in reliance on it. Verify property tax with the town assessor, financing with your lender, insurance with a licensed agent, and tax treatment with a CPA or attorney before you act on any number. Estimates are general guidance only. Property tax depends on the specific parcel, its assessment, exemptions, and any fire or special district levies; confirm with the town assessor. Insurance figures are modeled from structure value and water exposure and are no substitute for a quote. Maintenance reserves are planning estimates, not predictions. Mill rates are OPM FY 2025–2026 except where a panel states a confirmed FY 2026–27 rate. Median sale prices and median home sizes reflect current Market Pulse data. Not tax, legal, or insurance advice.