EMI Calculation (Problem in DataType)

This is my code
<pre>
Decimal Interest = 0;
EMICalculatorList ECL = new EMICalculatorList();
ProjectXBL.Config.EMICalculator EC;
int month = ddlMonth.SelectedValue.ToNonNullInt32() - 1;
Decimal Intr = 0;
Decimal Mth = txtPrinciple.Text.ToNonNullDecimal() / txtLoanDurationInMonths.Text.ToNonNullDecimal();
Decimal principalAmt = txtPrinciple.Text.ToNonNullDecimal();
Decimal ROI = txtAnnualInterestRate.Text.ToNonNullDecimal();
Decimal months = txtLoanDurationInMonths.Text.ToNonNullDecimal();
Decimal F = 1200;
for (int i = 0; i < txtLoanDurationInMonths.Text.ToNonNullInt32(); i++)
{
Intr = Intr + ((principalAmt * ROI) / F);
principalAmt = principalAmt - Mth;
}
Decimal Avg = Intr.ToNonNullDecimal() / txtLoanDurationInMonths.Text.ToNonNullDecimal();
Decimal MonthlyPayment = ((txtPrinciple.Text.ToNonNullDecimal() / txtLoanDurationInMonths.Text.ToNonNullDecimal()) + Avg).ToNonNullDecimal();
lblMonthlypaymentsText.Text = string.Empty;
lblMonthlypaymentsText.Text = Math.Round(MonthlyPayment, 2).ToString();
lblAnnulLoanPaymentsText.Text = string.Empty;
lblAnnulLoanPaymentsText.Text = Math.Round((MonthlyPayment * 12), 2).ToString();
Decimal Ending = 0;
Decimal Ints = 0;
Decimal Prnc = 0;
Decimal CumPrinc = 0;
Decimal CumIntr = 0;
Decimal principal = txtPrinciple.Text.ToNonNullDecimal();
for (int i = 0; i < txtLoanDurationInMonths.Text.ToNonNullInt32(); i++)
{
EC = new ProjectXBL.Config.EMICalculator();
//No,Month And Year
EC.No = i + 1;
if (month == 0)
{
EC.Year = txtYear.Text;
}
if (month == 12)
{
month = 0;
EC.Year = (txtYear.Text.ToNonNullInt32() + 1).ToString();
}
EC.Month = ddlMonth.Items[month].Text;
month++;
//
EC.Payment = MonthlyPayment;

Decimal monthly = principal / months;//Monthly payable without interest
EC.Interest = (principal * ROI) / 1200;
Ints = EC.Interest;
principal = principal - monthly;
Interest = Interest + EC.Interest;
EC.Principal = MonthlyPayment - EC.Interest;
Prnc = EC.Principal;
if (i == 0)
{
EC.BeginningBalance = txtPrinciple.Text.ToNonNullDecimal();
EC.CumulativePrinciple = EC.Principal;
EC.CumulativeInterest = EC.Interest;
}
else
{
EC.BeginningBalance = Ending;
EC.CumulativePrinciple = CumPrinc + Prnc;
EC.CumulativeInterest = CumIntr + Intr;
}
EC.Ending = EC.BeginningBalance - EC.Principal;
Ending = EC.Ending;
CumPrinc = EC.CumulativePrinciple;
CumIntr = EC.CumulativeInterest;
ECL.Add(EC);
}
lstEMI.DataSource = ECL;
lstEMI.DataBind();
</pre>

I solved this issue using javascript....