A method is provided for automatically updating a "Real Time" Average Speed of Answer, RASA, for a number of calls received by an automatic call distributor, ACD, during a set interval. This "real time" average speed of answer may be determined across a sliding time window via moving averages and exponential smoothing. The method includes the steps of computing a current average Speed of Answer, SA, for the number of calls received by the ACD during the set time interval, by dividing total waiting time to answer for these calls by the number of calls and scaling the current SA by a weight factor W. The real time average speed of answer, RASA, is updated by scaling a previous RASA by the unity complement of W, i.e. (1-W), and augmenting it by the scaled current SA.