What a house costs to hold

The mortgage payment is the small half of owning. The carrying costs are the half people forget, so the engine prices them explicitly rather than folding them into a fudge factor.

The formula

Each is a rate against the home's value, evaluated monthly:

property tax  = propertyTaxRate  × home value
maintenance   = maintenanceRate  × home value
insurance     = insuranceRate    × home value
utilities     = a flat monthly amount, indexed to inflation

The defaults, and what kind of number they are

The property tax rate is a published municipal figure. The 1% maintenance rule and the utilities estimate are convention, not law — widely used rules of thumb, cited to where they come from and labelled as conventions in the registry. The insurance rate is a band (roughly 0.1%–0.45% of value); a figure outside it is flagged so you check your quote rather than a default.

The two modelling choices worth knowing

• The basis. Rates are applied to the home's value, not to a fixed dollar amount, so every one of them rises as the home appreciates.
• Property tax tracks the home. That assumes your assessment moves with the market. Ontario reassessment is revenue-neutral, so an average bill really does track the municipal levy rather than the assessed value — but an unusual property will diverge.

Maintenance, insurance and utilities grow with inflation instead.