Keep or sell the House calculator

Every number on this page comes from the same simulation, run twice — once for selling, once for keeping — a month at a time for thirty years. Nothing is a rule of thumb. When you drag a slider, both futures are recomputed from scratch, which is why the chart moves the instant you let go.

The starting line

Both paths begin from the same place: what you would have today if you sold. That is the appraised value, less the cost of selling, less the mortgage balance, less whatever is still owed to your former partner. If you sell, that figure is cash in your hand on day one. If you keep the house, it is the equity you are sitting on, with the settlement still attached. Because it is identical either way, every result is shown net of it — you are looking at value created from here, not wealth you already had.

Selling

Your share goes straight into a broad index fund and compounds at the return you set. Each month you add the amount on the investment dial, growing with inflation. You pay rent from income; the portfolio is never touched to cover it. When the calculator values the portfolio it deducts capital gains tax on the growth, so the figure is what you could actually spend.

Keeping

The mortgage amortizes on its real schedule — interest on the outstanding balance, the rest to principal — until the loan is gone. Property tax, insurance and maintenance rise with inflation; maintenance is a percentage of the home's value. Tenants pay rent that also rises with inflation, less a vacancy allowance, and cost a little in utilities and wear. Income tax is charged on the rent after deducting the rented share of interest, tax, insurance, maintenance and depreciation. When the calculator values the house it assumes a sale: it deducts selling costs, the remaining mortgage, the settlement owed, depreciation recapture, and capital gains tax on whatever exceeds the primary-residence exclusion — an exclusion you keep only while you live there.

What the investment dials mean

They are literal. The amount you set is what goes into the market each month, on both sides. That is deliberate: it lets you compare like with like, and it means the housing choice is judged on its own merits rather than on how much you happen to save. It also means tenants change your monthly cost, not your net worth — the difference they make becomes wealth only if you choose to invest it, which the Keep column will tell you in dollars.

What it leaves out

Liquidity, which is worth a great deal in a bad year and nothing in a good one. The hours and the friction of being a landlord. The chance that the appraisal is wrong in either direction. Refinancing, a HELOC against the house, selling in five years rather than thirty, and any change to tax law. It is a projection built on the assumptions you can see on the left, and it is only as good as they are.

The defaults describe one real house in Boulder County, Colorado — the friend this was built for. Change them to yours; that is the point of the left-hand column. But it helps to know what they rest on.

Home appreciation, 4.0% a year. The FHFA All-Transactions House Price Index for Boulder County rose from 40.4 in 1985 to 288.8 in 2025 — a 5.0% compound annual rate over forty years, and 4.3% since 2000. Four percent is deliberately below both. Zillow showed Boulder home values down about 2% year over year in early 2026, which is the kind of stretch the lower figure is meant to absorb. Your county will differ; the FHFA publishes the index for every metro area.

Stock market return, 8.0% a year. A nominal figure, before inflation, for a broad US index fund — modestly below the long-run historical average. If you prefer to think in real terms, drop both this and home appreciation by the inflation rate; the comparison between them is what matters.

Selling costs, 7%. Agent commissions on both sides, title, transfer taxes and the small repairs a buyer's inspection turns up. Commission structures have been changing; if you have a firm quote, use it.

Maintenance, 0.6% of value a year. A long-run average for a house in good repair, not a monthly bill. Roofs and furnaces arrive in lumps. The common rule of thumb is 1%, and an older house earns it.

Vacancy, 8%. Roughly one empty month a year per room, which is what turnover between tenants tends to cost even when demand is strong.

Taxes. A 24% federal bracket plus Colorado's 4.4% flat rate on rental income; 15% federal plus state on long-term capital gains; 25% federal plus state on depreciation recapture. The $250,000 primary-residence exclusion is the single-filer amount. These are inputs, so set them to your own.

The settlement. The default treats what is owed to your former partner as a fixed sum, paid when the house eventually sells, with no interest. That is a favourable structure for the person keeping the house and not every decree allows it. If yours requires payment now, model it as a loan at today's home-equity rates — the Keep column shows what that adds per month.

Should I keep the house or sell it in a divorce?

It comes down to four things the calculator makes explicit: the rate on your existing mortgage, whether you can carry the house with tenants, how the settlement is structured, and how long you intend to stay. A low-rate mortgage and a deferred, interest-free settlement favour keeping. A short horizon, no appetite for tenants, or a settlement you would have to borrow to pay favour selling. Run it both ways and look at the five- and ten-year cells, not just the thirty-year one.

Why does keeping win early and selling win late?

While the mortgage is being paid down, each payment converts cash into equity on a leveraged asset, and a 3% loan is cheap money. Once the loan is gone, the house just tracks appreciation, while the index fund keeps compounding at a higher rate. Whether the crossover matters depends entirely on whether you would actually still own the house in year twenty-five.

Why doesn't changing the interest rate move the thirty-year result?

Because the mortgage is fully repaid within its term in every scenario, so by year thirty the rate has stopped mattering. It matters a great deal in between: it changes what you pay every month and where you stand at five, ten and fifteen years. Watch those cells.

Why doesn't the number of tenants change my net worth much?

Because you set what you invest each month directly. Tenants lower what the house costs you; that only becomes wealth if you invest the difference. The Keep column tells you the monthly saving between one tenant and a full house so you can move the dial by exactly that amount if you want to see it compound.

What if I have savings outside the house?

Add them to both sides equally in your head — they compound the same either way and cancel out of the comparison. The calculator deliberately models only the house decision. The one case where outside savings change the answer is if they let you pay the settlement in cash rather than borrowing it; set the "owed at sale" input to zero and raise the sell-side day-one figure accordingly.

Can I use this if we aren't divorcing?

Yes. Set the amount owed to zero and it is a plain keep-versus-sell comparison for any house you could rent rooms in, with the same tax treatment and the same honest accounting.

Is anything I type saved or sent anywhere?

No. Everything runs in your browser. There is no server, no account and no analytics of our own. The only thing stored is your mood choice, in your own browser, so the page looks the same next time. Ads, when present, are served by third parties under their own policies — see the privacy page.

Is this financial or legal advice?

No. It is arithmetic, done carefully, on assumptions you control. The capital-gains, depreciation-recapture and settlement questions deserve a CPA and a family-law attorney before anything is signed. Bring them the printout; it makes the conversation faster.