1. A controller for presenting an estimate of fault cost in a building management system comprising: a processing circuit configured to maintain a history of energy usage values for the building management system and a threshold parameter relative to the history of energy usage values; and wherein the processing circuit is further configured to identify energy outlier days by comparing energy use for a day to the history of energy usage values and the threshold parameter; wherein the processing circuit is further configured to subtract an estimated average daily cost, calculated with the outlier days, from an estimated average daily cost calculated excluding the outlier days to estimate an additional cost of the energy outlier days; wherein the processing circuit is configured to assign the estimated additional cost of the energy outlier days to the estimate of the fault cost in the building management system; and wherein the processing circuit is configured to output the estimated fault cost to at least one of a remote device and a local electronic display.