Vacancy rate is the percentage of time a rental unit sits empty between tenants, expressed as a percent of potential rent lost. Even strong rental markets typically see 3-8% vacancy once you account for tenant turnover, marketing time, and move-in/move-out gaps — modeling 0% vacancy overstates your real return.
CapEx/maintenance reserves are money set aside monthly (rather than only spent reactively) for large, infrequent costs — roofs, HVAC, water heaters, appliances — so a single big repair doesn't wipe out a year of cash flow. A common starting rule of thumb is 5-15% of rent depending on the property's age and condition, adjusted from actual inspection findings when available.