Financial.Rate Method (Double, Double, Double, Double, DueDate, Double)
Note 

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Returns a Double specifying the interest rate per period for an annuity.
Assembly: Microsoft.VisualBasic (in Microsoft.VisualBasic.dll)
public static double Rate( double NPer, double Pmt, double PV, double FV = 0, DueDate Due = DueDate.EndOfPeriod, double Guess = 0.1 )
Parameters
 NPer

Type:
System.Double
Required. Double specifies the 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 * 12 (or 48) payment periods.
 Pmt

Type:
System.Double
Required. Double specifies the payment to be made each period. Payments usually contain principal and interest that doesn't change over the life of the annuity.
 PV

Type:
System.Double
Required. Double specifies the 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

Type:
System.Double
Optional. Double specifies the future value or cash balance you want after you make the final payment. For example, the future value of a loan is $0 because that is 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

Type:
Microsoft.VisualBasic.DueDate
Optional. Object of type DueDate 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.
 Guess

Type:
System.Double
Optional. Double specifying value you estimate is returned by Rate. If omitted, Guess is 0.1 (10 percent).
Return Value
Type: System.DoubleReturns a Double specifying the interest rate per period for an annuity.
Exception  Condition 

ArgumentException  NPer <= 0. 
An annuity is a series of fixed cash payments made over a period of time. An annuity can be a loan (such as a home mortgage) or an investment (such as a monthly savings plan).
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.
Rate is calculated by iteration. Starting with the value of Guess, Rate cycles through the calculation until the result is accurate to within 0.00001 percent. If Rate cannot find a result after 20 tries, it fails. If your guess is 10 percent and Rate fails, try a different value for Guess.
This example uses the Rate function to calculate the interest rate of a loan given the total number of payments (TotPmts), the amount of the loan payment (Payment), the present value or principal of the loan (PVal), the future value of the loan (FVal), a number that indicates whether the payment is due at the beginning or end of the payment period (PayType), and an approximation of the expected interest rate (Guess).
Sub TestRate() Dim PVal, Payment, TotPmts, APR As Double Dim PayType As DueDate ' Define percentage format. Dim Fmt As String = "##0.00" Dim Response As MsgBoxResult ' Usually 0 for a loan. Dim FVal As Double = 0 ' Guess of 10 percent. Dim Guess As Double = 0.1 PVal = CDbl(InputBox("How much did you borrow?")) Payment = CDbl(InputBox("What's your monthly payment?")) TotPmts = CDbl(InputBox("How many monthly payments do you have to make?")) Response = MsgBox("Do you make payments at the end of the month?", MsgBoxStyle.YesNo) If Response = MsgBoxResult.No Then PayType = DueDate.BegOfPeriod Else PayType = DueDate.EndOfPeriod End If APR = (Rate(TotPmts, Payment, PVal, FVal, PayType, Guess) * 12) * 100 MsgBox("Your interest rate is " & Format(CInt(APR), Fmt) & " percent.") End Sub
Available since 1.1