Adding new item to list time complexity

[night stream]

template<typename T>
void List<T>::push_back(T data)
{
if (m_Head == nullptr)
m_Head = new Node<T>(data);
else
{
Node<T>* current = m_Head;

    while (current->pNext)
        current = current->pNext;

    current->pNext = new Node<T>(data);
}

}

Why people say that time complexity for adding new element to list is O(1) when here we have to iterate through the list to add new element, so shouldn`t it be O(n)?

[final apex]

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[heady coral]

Lists store the length of the list as a field. So assuming the appended item will fit the current allocated memory for the list no iteration is needed.