How does the "X day within Y month" works ?

Hi,

I don’t quiet understand how the travelling days are counted.

I’ll try to explain.

Let’s say I’m in Paris, and want to go to Milano for 5 nights, then Verona for 2 nights, then Roma, again 5 nights, Genova, for another 5 nights, and go back to Paris.

So Paris => Milano => Verona => Roma => Genova => Paris. I would be taking the train 5 times, so I could take the “5 days within a month” pass.

But, when I use the tripplaner here https://www.interrail.eu/en/tripplanner-map , it seems than I can’t have access to this pass, since it is noted that I would need 9 days of travel.

Do I miss something ?

Thank you very much for your help !