Abstract: In a method and apparatus for managing and calculating interest on time deposits, loans, and other interest bearing financial instruments, data is stored in several distinct memories. A series of financial transactions is stored in a transaction memory having date and principal amount attributes. Data representing the performance of an investment or loan is stored in an interest factor memory having date, interest factor, and aggregate factor attributes. A displayable interest data memory is populated with interest data synthesized by associating the transaction memory to the interest factor memory by matching corresponding date attributes, then computing the product of the transaction principal amount attribute in the transaction memory and the aggregate factor attribute in the interest factor memory.