{T}: You gain 1 life. Then if you have at least 10 life more than your starting life total, transform Chalice of Life.
For more information on double-faced cards, see the Shadows over Innistrad mechanics article (http://magic.wizards.com/en/articles/archive/feature/shadows-over-innistrad-mechanics).
You check your life total to see if Chalice of Life transforms only when its ability resolves.
Your starting life total is the life total you began the game with. For most two-player formats, this is 20. For Two-Headed Giant, it’s the life total your team started with, usually 30. In Commander games, the starting life total is 40.