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IPmt Function
Returns a Double specifying the interest payment for a given period of an annuity based on periodic, fixed payments and a fixed interest rate.
Function IPmt( _ ByVal Rate As Double, _ ByVal Per As Double, _ ByVal NPer As Double, _ ByVal PV As Double, _ Optional ByVal FV As Double = 0, _ Optional ByVal Due As DueDate = DueDate.EndOfPeriod _ ) As Double
Parameters
 Rate

Required. Double specifying interest rate per period. For example, if you get a car loan at an annual percentage rate (APR) of 10 percent and make monthly payments, the rate per period is 0.1/12, or 0.0083.
 Per

Required. Double specifying payment period in the range 1 through NPer.
 NPer

Required. Double specifying total number of payment periods in the annuity. For example, if you make monthly payments on a fouryear car loan, your loan has a total of 4 x 12 (or 48) payment periods.
 PV

Required. Double specifying present value, or value today, of a series of future payments or receipts. For example, when you borrow money to buy a car, the loan amount is the present value to the lender of the monthly car payments you will make.
 FV

Optional. Double specifying future value or cash balance you want after you've made the final payment. For example, the future value of a loan is $0 because that's its value after the final payment. However, if you want to save $50,000 over 18 years for your child's education, then $50,000 is the future value. If omitted, 0 is assumed.
 Due

Optional. Object of type DueDate Enumeration that specifies when payments are due. This argument must be either DueDate.EndOfPeriod if payments are due at the end of the payment period, or DueDate.BegOfPeriod if payments are due at the beginning of the period. If omitted, DueDate.EndOfPeriod is assumed.
Exception type  Error number  Condition 

Per <= 0 or Per > NPer 
See the "Error number" column if you are upgrading Visual Basic 6.0 applications that use unstructured error handling. (You can compare the error number against the Number Property (Err Object).) However, when possible, you should consider replacing such error control with Structured Exception Handling Overview for Visual Basic.
An annuity is a series of fixed cash payments made over time. An annuity can be a loan (such as a home mortgage) or an investment (such as a monthly savings plan).
The Rate and NPer arguments must be calculated using payment periods expressed in the same units. For example, if Rate is calculated using months, NPer must also be calculated using months.
For all arguments, cash paid out (such as deposits to savings) is represented by negative numbers; cash received (such as dividend checks) is represented by positive numbers.
This example uses the IPmt function to calculate how much of a payment is interest when all the payments are of equal value. Given are the interest percentage rate per period (APR / 12), the payment period for which the interest portion is desired (Period), the total number of payments (TotPmts), the present value or principal of the loan (PVal), the future value of the loan (FVal), and a number that indicates whether the payment is due at the beginning or end of the payment period (PayType).
Sub TestIPMT() Dim APR, PVal, Period, IntPmt, TotInt, TotPmts As Double Dim PayType As DueDate Dim Response As MsgBoxResult ' Usually 0 for a loan. Dim Fval As Double = 0 ' Define money format. Dim Fmt As String = "###,###,##0.00" PVal = CDbl(InputBox("How much do you want to borrow?")) APR = CDbl(InputBox("What is the annual percentage rate of your loan?")) If APR > 1 Then APR = APR / 100 ' Ensure proper form. TotPmts = CInt(InputBox("How many monthly payments?")) Response = MsgBox("Do you make payments at end of the month?", MsgBoxStyle.YesNo) If Response = MsgBoxResult.No Then PayType = DueDate.BegOfPeriod Else PayType = DueDate.EndOfPeriod End If For Period = 1 To TotPmts ' Total all interest. IntPmt = IPmt(APR / 12, Period, TotPmts, PVal, Fval, PayType) TotInt = TotInt + IntPmt Next Period ' Display results. MsgBox("You will pay a total of " & Format(TotInt, Fmt) & _ " in interest for this loan.") End Sub
Namespace: Microsoft.VisualBasic
Module: Financial
Assembly: Visual Basic Runtime Library (in Microsoft.VisualBasic.dll)