A license start at the day you purchase it and is valid for the period you have chosen.
It doesn't matter when you start using the license.
Hello,
It's what it said when we purchase , but it's not pretty what happens (at least for me and 8 years renews)
ex:
I just purchase my 3pc/2y october 11th (Digital River)
Previous licence end october 19th (same 1 week purchase before end ,2 years ago october 11th 2014)
The "D" day was , is , and will be (Avast UI interface) october 19th .
Edit:however , on my DR account it's indicated october 11th 2018 unlike on my.avast account october 19th 2018
Even if DR answer my e-mail last week to say 11th , the main and essential is avast who say 19th