Another infinite loop

[wlsa]

Fixed it, thanks for all your help. In the end I used this.

monthlyInterestrate=annualInterestRate/12
balance_initial=balance
lowerbound=(1/12)*balance
upperbound=balance*(1+monthlyInterestrate)**(12)/12
while balance >.0001 or balance<-.0001:
    balance=balance_initial
    monthlyPayment=(upperbound+lowerbound)/2
    for i in range(12):
        balance=balance-monthlyPayment + (balance-monthlyPayment)*monthlyInterestrate
    if balance>0:
            lowerbound=monthlyPayment
    if balance<0:
            upperbound=monthlyPayment
     
print('Lowest Payment: ' + str(round(monthlyPayment, 2)))