Why does it start at 1200

0 would only corresspond to someone who knew nothing of chess.  That's not the case for most people who join chess.com-- most of them already at least know some, if not most, of the rules, and some people are already quite good players even though they don't yet have chess.com ratings.  Apparently 1200 is considered a good initial middle-of-the-road "guess" for a new member's rating, and from that point it can move in either direction as more input on the player's ability becomes available from their game play.

best comment I have ever read in chess.com

i played some chess when i was a kid, i enjoy it today, i know how to play, I'm 925.....this is the correct place to start new people at, or maybe 100

i could cheat and keep creating new accounts and wasting 1200's time by playing in games i haven't earned the right to be in. please start new accounts at the bottom

because if you play chess as well as i do, you don't deserve to have fun

Coz why not ?

because you start at intermedate

But I also see ppl starts at 400???

If you want to know your rating based on a zero scale, subtract 1200.

I assume that level of math is not above your ability.

Many people come to chess.com after they learn and play chess irl. So it wouldn't make sense for them to start at 0 (or 100, in this case).

This thread started in 2011. Initial ratings were set at 1200 then.

That is no longer the case.

Players are asked about their experience level when they join now and can start at 400, 800, 1200 or 1600.

If they misrate themselves, the rating will soon adjust to the proper level.