In most countries, unfortunately none of the eight Harry Potter films are available for streaming on Netflix, or any of the other major subscription services, like Now TV or Amazon Prime.
The movies have been such a huge success for Warner Bros., which distributes them in the UK and abroad. It's currently the highest-grossing film series of all time (though will probably be overtaken by the Marvel Universe next year), with more than $7.5 billion in the bank from cinema tickets alone.
Because it's so popular, Warner Bros. Know that they can still make a lot of money selling the film on DVD and Blu-ray, and so haven't made it available for streaming services like Netflix, because they would effectively lose money by doing so.
A few of the films in the series - Harry Potter and the Chamber of Secrets and Harry Potter and the Prisoner of Azkaban, for example - are streaming on Netflix in a couple of countries, like Mexico or Brazil. So unless you're streaming from either of those countries, it's likely that the only way you'll be able to watch the movies is to buy or rent them.
Here's a video combining a trailer for each film to help you decide if you might want to spend more money to buy them.
