Another infinite loop

[wlsa]

I edited my code to

annualInterestRate=.1
balance=100
monthlyInterestrate=annualInterestRate/12
balance_initial=balance
lowerbound=(1/12)*balance
upperbound=balance*(1+monthlyInterestrate)**(12)/12
monthlyPayment=(upperbound+lowerbound)/2
while balance>-.00001 and balance<.00001:
    for i in range(12):
        balance=balance-monthlyPayment + (balance-monthlyPayment)*monthlyInterestrate
    if balance>0:
            monthlyPayment=(upperbound+monthlyPayment)/2
    if balance<0:
            monthlyPayment=(lowerbound+monthlyPayment)/2
    
print('Lowest Payment: ' + str(round(monthlyPayment, 2)))

but now everything is off by a small amount.
For instance, a balance of 320000 and an annualInterestRate of .2 should yield "Lowest Payment: 29157.09" but I'm getting 29591.88

I'm quite confused as to why this still isn't working.