I have a 5-year Type-C Schengen visa and I went to the Netherlands on October 17, 2017 for approximately two months. After that I haven't been to any Schengen country until today. Currently I am planning to go to the Netherlands again on August 10, 2018. Am I allowed to enter the Netherlands without applying for another visa? I am not sure about this 180/90 days rule.
Thank you.
If your visa is still valid (and will remain valid for the entirety of the stay you're planning), then it will be valid for your next stay.
"Approximately two months" after 17 October 2017 is somewhen in mid-December 2017. If you have been outside Schengen since then, much more than 180 days will have passed when you enter in August 2018, and you will have no problems at all with the 90/180 day rule.
(In fact, even being outside the Schengen area for 90 consecutive days is enough to make all previous travel irrelevant for the purpose of the 90/180 day rule, but in your situation you don't need to understand the subtleties of why that is true).
