I am trying to create a formula to forecast a decrease to the per unit rental rate of widgets. For the first 12 months, each widget costs $100 per month. From months 13 on, each widget costs $75 per month. However, the widgets can be ordered at any time. For example, 100 may be ordered on 10/1/2014, another 50 may be ordered on 11/15/2014, followed by 30 more on 12/1/2014, etc. Due to the different initial order dates, the rate reduction will obviously occur at different times. Does anyone have an idea on how this could be captured in an overall forecast/budget without me needing to constantly track each individual widget? Thanks for the help!