Rent versus buy: the assumptions that move the result

This guide explains how PROPIQ defines a calculation. Verify figures before any purchase.

Renting and buying are not compared by a single 'correct' number. The PROPIQ scenario compares two stories that share one pool of cash at the start: the down payment plus the upfront costs you type.

In the renting story, that cash is invested at an opportunity-cost rate you choose. Each year, rent grows from the starting rent at a growth rate you choose. In the buying story, that opening cash is spent. The property value changes at an appreciation rate you choose. A loan, if you enter one, is a standard principal-and-interest schedule. Service charge, maintenance, and insurance stay flat unless you change the inputs. They are not inflated for you, because an invented inflation rate would look like a forecast.

At the start of each year, both cash pots grow by the opportunity-cost rate. Whoever spends less that year is modeled as investing the difference at the end of the year. At the horizon, buyer wealth is the cash pot plus the property value, minus a selling-cost assumption, minus the remaining loan. Renter wealth is the cash pot. Cumulative rent is shown as money spent, not as an asset.

Taxes, early-repayment charges, irregular repairs, and rules about who may buy are outside the formula unless you have already put them inside a number you typed. A positive or negative gap shows how this scenario compares; verify the figures before any purchase.

The horizon must be at least one year. A down payment cannot exceed the price. A growth rate of -100% or worse is rejected because the series collapses. Those checks are there so the tool fails visibly instead of showing a nonsense figure.