Computer systems and methods enable an Individual to simulate real estate/financial transactions over time, provide accounting and cash flow management for management of real estate investments, track property values for rental propelties taking into account tenant creditworthiness (tenant credit score), and import information related to real property units under consideration for purchase from a list of available real property units available for sale and to compare the real property units. The computer system calculates a tenant reliability score (TRS) that is incorporated by a simulator into cash flow projections such that the investor could compare different potential tenants.