A renter who actually invests the cash a buyer would tie up in a down payment isn’t losing that money — they’re compounding it somewhere else instead of in home equity.
Comparing monthly rent to a mortgage payment alone misses the opportunity cost on both sides — the honest comparison nets out total cash spent against equity built (for buying) or investment growth (for renting), and the assumed investment return often decides which one wins.
Estimate with the rule, then check it against the calculator that models it properly.
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