Below is my code to calculate interest and balances and how many months to get there. However, my months calculations are way off by the thousands. Any idea?

```
#include<iostream>
#include<string>
#include<cmath>
using namespace std;
class Account
{
public:
Account();
Account (double bal);
void deposit(double amount);
void withdraw(double amount);
double get_balance() const;
void add_interest(double rate);
private:
double balance;
};
Account::Account()
{
}
Account::Account(double bal)
{
balance = bal;
}
void Account::deposit(double amount)
{
balance +=amount;
}
void Account::withdraw (double amount)
{
if ( balance >= amount)
balance -= amount;
else
balance -= 5.00; // Charge a $5.00 penalty fee if attempting to withdraw more than balance.
}
double Account::get_balance()const
{
return balance;
}
void Account::add_interest(double rate)
{
balance *= ( 1 + (rate/100.0));
}
int main()
{
cout << " Enter initial investment: ";
double initial_investment;
cin >> initial_investment;
cout << " Enter annual interest rate in percentage: ";
double rate_in_percentage;
cin >> rate_in_percentage;
double monthly_rate = rate_in_percentage/100.0/12.0;
double final_amount = 2 * initial_investment;
Account my_account(initial_investment);
int months = 1;
//
// one iteration of the loop corresponds to one month
//
while ( my_account.get_balance()<final_amount)
{
my_account.add_interest(monthly_rate);
months++;
}
cout << " It took " << months << " months for $ " << initial_investment <<
" to double at " << rate_in_percentage << "% annual interest. \n";
cout << " Account balance: " << my_account.get_balance() << "\n";
return 0;
}
```