Why Different Rent vs. Buy Calculators Give You Different Answers
Rent vs. buy calculators disagree mainly because of differing default assumptions for home appreciation rate, investment return on the renting side, and ongoing maintenance cost — all three are genuine unknowns about the future, not fixed facts, so reasonable tools can use different reasonable defaults and reach different conclusions.
Two rent-vs-buy calculators can take nearly identical inputs — same home price, same rent, same rate — and still disagree, and the reason is almost always in the assumptions running quietly in the background rather than in the core math.
The three assumptions that swing the answer most
Home appreciation rate: a difference of even 1–2 percentage points in assumed annual appreciation compounds significantly over a decade or more, and there's no single correct number — it depends on the local market and time period.
Investment return on the renting side: the money not spent on a down payment is assumed to be invested — the assumed return rate on that investment (conservative vs. optimistic) meaningfully shifts how competitive renting looks.
Maintenance and repair costs: commonly estimated as roughly 1% of home value per year, but real maintenance costs vary a lot by home age and condition — a tool defaulting to a lower maintenance estimate will favor buying more than one using a higher one.
How to compare tools fairly
Rather than trusting one tool's default assumptions, it's worth checking whether a calculator lets you adjust appreciation rate, investment return, and maintenance cost explicitly — and running the same set of assumptions through more than one tool to see whether the disagreement was really about the math, or just about the defaults.