How the comparison is actually made
Comparing renting with buying by putting a rent figure next to a mortgage payment is not a comparison, because the two payments buy different things and neither includes the full cost. This calculator instead simulates both paths month by month over the number of years you plan to stay, and compares the wealth each path leaves you with at the end.
The owner path starts by spending the down payment and the buying costs. Each month it pays the mortgage, property tax computed as a percentage of the current home value, and maintenance computed the same way. The home appreciates monthly at the annual rate you enter, converted to a monthly equivalent. At the end of the period the home is sold, selling costs are deducted, the remaining loan is repaid, and the net proceeds are owner wealth.
The renter path starts by investing what the buyer spent up front, the down payment plus buying costs, at the investment return you specify. Each month the renter pays rent, which grows at the rent growth rate. Whenever the owner's monthly cost exceeds the rent, the renter invests the difference; whenever rent exceeds the owner's cost, the owner invests the difference. That symmetry is what makes the comparison fair: the person with the lower monthly outlay is assumed to invest the savings rather than consume them.
Worked example: a 500,000 home versus 2,000 a month rent
Using the calculator defaults of a 500,000 home, 20 percent down, a 6 percent mortgage over 30 years, 2,000 monthly rent, 3 percent annual rent growth, 3 percent annual appreciation, a ten year stay, 1.2 percent property tax, 1 percent maintenance, 3 percent buying costs, 6 percent selling costs, and a 6 percent investment return, the mortgage payment is 2,398.20 on a 400,000 loan.
First month owner cost is 2,398.20 in mortgage, plus 500.00 in property tax (500,000 * 0.012 / 12), plus 416.67 in maintenance (500,000 * 0.01 / 12), for 3,314.87. Rent in the same month is 2,000, so the renter invests the 1,314.87 difference on top of the 115,000 already invested, which is the 100,000 down payment plus 15,000 in buying costs.
After ten years the home is worth 671,958 and the loan balance is 334,743. Selling at 6 percent cost leaves net proceeds of 296,898, which is owner wealth. The renter's portfolio has grown to 393,959. On these assumptions renting comes out ahead by about 97,062 over the ten years. Changing the investment return to 3 percent, or the appreciation to 5 percent, flips the result, which is the point: the answer lives in the assumptions.
Which inputs move the answer most
The three that dominate are home appreciation, the investment return, and the number of years you stay. Appreciation and investment return are the growth rates applied to the two competing pools of capital, and the comparison is largely a race between them. Setting them equal removes the leverage argument for buying almost entirely, since the buyer's advantage comes from appreciation applying to the whole home value rather than only to the equity.
Years of stay matters because the transaction costs are front loaded and back loaded. Three percent to buy and six percent to sell is nine percent of value consumed by the round trip, which on a 500,000 home is roughly 45,000 before any appreciation. Short stays rarely recover that. Lengthening the stay spreads those costs and gives appreciation more time to work.
Rent growth is the quiet one. At 3 percent, rent doubles in about 24 years, while the mortgage principal and interest portion is fixed for the whole term. Over a long enough horizon this alone tends to favor buying, which is why the same inputs can say rent at five years and buy at twenty.
What the model excludes
Taxes are excluded on both sides. The mortgage interest and property tax deductions are not modeled, which understates the owner's position for households that itemize. Neither are capital gains taxes on the renter's investment portfolio or the primary residence exclusion on the home sale, which run in opposite directions. Modeling any of these accurately would require your filing status and bracket.
Homeowners insurance, HOA dues, and renters insurance are not separate inputs. The maintenance percentage is the only recurring ownership cost besides tax and mortgage, so if you want insurance and HOA covered, raise the maintenance figure accordingly. A 1 percent maintenance assumption is a common rule of thumb and is not based on your specific property.
The model also assumes rent and ownership are otherwise equivalent, which they are not. It cannot price the security of a fixed housing cost, the constraint of being tied to a property, the risk of a rent increase or a non renewal, or the possibility of a forced sale into a weak market. It is a financial comparison of two capital paths, and the non financial differences are real.
The mistake people make with rent versus buy
The largest mistake is leaving the investment return at zero or ignoring it, which assumes the renter spends every dollar of the difference. If the renter genuinely does spend it, then buying is a forced savings mechanism and wins for behavioral reasons rather than financial ones. That is a legitimate argument, but it should be made explicitly rather than hidden in an assumption.
The second is using an optimistic appreciation rate drawn from a recent boom. Long run US home price appreciation has historically been closer to inflation than to equity returns, with long flat stretches in real terms. Entering 7 or 8 percent produces a decisive answer for buying that is an artifact of the input.
The third is ignoring the exit costs. Six percent selling costs on an appreciated home is a large number, and buyers who expect to move within three or four years often find that the round trip consumed the entire gain. Run the calculator at your realistic time horizon rather than at thirty years, then run it again a few years shorter to see how fragile the answer is.