def METHOD_NAME(start_date, end_date, date_format="%d-%m-%Y", default_tz=timezone.utc):
    """
    Calculates the difference in days between a start date and an end date.
    :param start_date: The start date. May be a datetime instance, a unix timestamp or a string representation of a date.
    :param end_date: The end date. May be a datetime instance, a unix timestamp or a string representation of a date.
    :param date_format: If one or both date values are provided as strings, the date format which is needed for conversion.
    Default: "%d-%m-%Y"
    :param default_tz: Timezone to use for dates using unix timestamp or not already specified in date_format
    Default: timezone.UTC
    :return: The difference between start and end date in complete days.
    """
    start = _to_datetime(start_date, date_format, default_tz)
    end = _to_datetime(end_date, date_format, default_tz)
    return (end - start).days