How often do I Purge Cache on Cloudflare?

I see the option on my Cloudflare Dashboard to purge the cache, so it receives my most up to date website info, but how often does Cloudflare update the cache automatically without me having to purge cache each time I update my website?

By default, the cache only caches static resources like images, css and js files, not html.
See here for a full list:

So if you did not force html caching, you don’t need to purge the cache for normal content updates like blog posts.

You would usually purge the cache if you make changes to the site itself, like changing the theme.