Google makes tweaks and updates all the time that we don't even know about. Keep in mind that Google is not the only source of traffic.
At this point in time Google does new updates all the time. I don't think they really announce new updates anymore. Instead, they just push them out on almost a daily basis.
Google recently update their panda algo on 18th July and they said it's really a slow update. it's affected about 2%–3% of English language queries.
Hi on 24 April there is Panda Refresh....you can see the no of threads on webmaster forum..... here is link for more information https://www.seroundtable.com/google-panda-refresh-gary-confirm-20647.html
There's some misinformation in this thread- In short, nobody knows except the Google engineers. It could be minutes, hours, days, weeks, months, years before another. The only real way of being 'ahead of the curve' is to keep updated on the various SEO news / discussion channels. (seroundtable, searchengineland, etc.) Keep in mind Panda is supposedly still rolling out as we speak.
More info http://searchengineland.com/google-panda-4-2-is-here-slowly-rolling-out-after-waiting-almost-10-months-225850 Code (markup):