def pro_rata_monthly_charge(monthly_charge: float, days: int) -> float:
    """ The monthly or annual charges shall be calculated pro rata having
    regard to the number of days in the billing cycle that supply was
    connected (days) and one-twelfth of 365.25 days (to allow for leap years).

    monthly_charge: The monthly charge
    days: The number of days in the billing period
    """
    daily_charge = (monthly_charge * 12) / 365.25
    return daily_charge * days