If I upgrade to Yosemite from ML will I lose everything?

[Sensamic]

Fast question. I'm on Mountain Lion. If I upgrade using the Mac App Store way would I lose all my already installed apps and documents?

Thanks.

 

[Bending Pixels]

Nope - but....always do a backup before upgrading.

 

[Sirious]

You won't lose anything, but you should still back up your most important files to an external source.

 

[Partron22]

My Time Machine Archive went south when I updated, inaccessible.
That's not a common problem, but it can happen.
I'm glad I made a full backup to a non Time machine partition as well.