The answer to this question varies greatly, because this period depends on the circumstances, the personal characteristics, the relationship we had, the way in which the loss happens etc. However, the first year is always very difficult, since everything reminds us of the deceased and as certain special dates go by: the first Christmas, the first birthdays, the first holidays etc.
The despair of not being able to share the events, achievements and feelings with that person make us relive the tragedy relentlessly. However, it is true that this period is not a passive one because it helps us to accept death and, slowly but surely, to live with it.