Returns the net present value (NPV) of a series of unequal payments made at regular intervals, assuming a fixed interestRate per interval.
payment - a repeating field containing unequal payment amounts, or an expression that returns a reference to one.
interestRate - interest rate.
Data type returned 
Originated in 
FileMaker Pro 6.0 or earlier
Use this function to calculate NPV. For example, if someone borrows money from you and pays you back in unequal amounts over a period of several years, you can use the NPV function to calculate the result.
NPV(Loan;.05) returns 156.91277445..., when the repeating field, Loan, contains -2000 (the initial payment), 600, 300, 500, 700, and 400. The result (156.91277445...) is the actual profit in today’s dollars that will be realized from this transaction.
NPV(Amounts;.10) returns 16758.35604870..., when the repeating field, Amounts, contains -5000 (the initial investment), 10,000, 0, 10,000, and 10,000.
If you want each return value to return 2 decimal places, surround the current formulas with the correct Round function: Round(Current Formula;2).
Related topics 
Functions reference (category list)
Functions reference (alphabetical list)
About formulas
About functions
Defining calculation fields
Using operators in formulas