Customers of shared resources or services can be informed of unusual variations in cost patterns over at least one determined period, in order to prevent those customers from being surprised upon receiving a significantly larger (or smaller) bill than expected. The daily cost (or portions of the daily cost) for a customer can be compared against the previous day's cost to determine a percentage cost variation. This cost variation can be compared against the mean of the percentage daily cost variations over a previous period, such as the last thirty days, to determine whether the variation falls outside a standard deviation (or other such threshold) from the mean. If so, the cost variation can be determined to be unusual, and the customer notified. The variation can be analyzed using daily, weekly, and monthly periods in order to identify unusual accumulations of small variations as well.