I have worked though this in a few different ways and had little luck identifying where i'm being a bone head. Here is what I have.
SharePoint List with column Date_received data type is date
Same list has column named storage Data type is Currency
If the item is received on or before day 15 of the month the value of storage should be 7 if received after the 15th day the value should be 3.50.
=if(DAY([Date_Received]<=15,3.50,7.00))
This is one of many variation of the formula I have used All provide a syntax or not supported error after clicking OK.