When to say, "I love you"

There is no perfect time to say, "I love you."  There are near perfect times often enough though.

For starters, do not say it too soon.  Saying it on a first date, ala Ted, on his first date with Robin on season one of How I Met Your Mother (for those of you not in the know, watch it here).

You do not love someone that early on, and even if you think you do, you do not tell the other person, unless you want to totally scare them away.

On the other hand, do not be one of those stubborn people who wait for the person you are with to say, "I love you" first.  Why? Because they might be just as stubborn as you.  This is love, not war.  We are not going for a stalemate.  

Simply, let your relationship with someone grow over time, at least a few months or more, and if you continually feel just as strong towards that person as from the start, or stronger, and you desire to share this warm feeling with them, then you can tell him/her.  

At this point, if you have been dating exclusively for that time period, it should be safe.  While this does not guarantee they will say it in return, or that things may not be slightly awkward for a bit, it should not ruin things. 

If your partner does not feel like it is "love" yet, or is scared to say it, they will just kindly let you know.  Do not take this as a sign that it is over, or that you should give up.  Just see that you need to forget saying those words again until they are comfortable saying them to you first.