Because of inflation, operating expenses rise each year, so owners need to raise rents in line with both the market and consider retaining their residents. Resident retention (renewal rates at lease expiration) matters because vacancy often costs 2-3 months of rent, and make-ready costs can be 1-2 months of rent. So any move-out costs consume rent increases. If the increase is too large, it can cause the tenant to look for a new home elsewhere. This calculator runs the full chain of events to help build intuition about each lever: the unit-level payback, the 12-month portfolio cash flow against doing nothing, and the three-year NOI picture once OPEX inflation is considered. Every input recomputes live.