Hello, I just need some clarification.
I had a multiple entry visa that expired on June 24th 2019 and I visited for 72days(april-june 2019)
I have heard that when I apply for a new visa my days reset, is this true? Or do I only have 18 days left if I apply for a new visa?
Thank you in advance

As far as I understand it, expired is expired.

Had you had a visa, let's say, for the entire month starting on 1st May and expiring on 31st May, but you never used it to enter the country at all, then you don't have 31 days "visa credit" for any other month. The visa grants you permission to enter the country between the starting date and up until the ending date. Thereafter it is over.

So yes, if your visa expired on 24th June, then you no longer have a visa, and you also no longer have those 18 days that you didn't use on that visa. You must leave the country.

Now, if you set about applying for a new visa, then those 18 days you didn't use are over/past/finito/gone and have no bearing at all on any new visa.

However, you may well have to be out of the country for a certain time before a new visa application will be considered [favourably].

Thank you that's what makes sense to me too. I am out of the country but I would like to go back again soon, so I just want to make sure that if I apply for a new visa I will be able to enter the country for the 3 months again or if I have to wait for the 180 days to pass before thinking of going applying for another visa to back to Switzerland again.

Maybe this will answer your question...
https://www.englishforum.ch/permits-...ay-period.html

Also, while you're in this thread, and scroll right down to the bottom of the page, it will suggest other, similar threads to you.
Do that in each of the others you look at, and the forum will walk you through more similar threads.

90 days within any period of 180 days unless a visa specifically allows otherwise. A new entry visa will not reset this.

No more, no less.