Why does my opponent sometimes automatically get extra time and I don't?

So I've been playing some 1 min games. Especially in one (rated) game when I was up in material and winning, I lost because the stupid computer or something added an extra 10 seconds to his time.  

Before the time somehow changed, I had a queen for a knight, was up in material, and was about 9-10 sec ahead in time. I was clearly going to win.

Then some computer/someone added 10 sec to my opponent's time. I just had to go on with the game.

I lost on time and he had 2 seconds left at the end of the game. And I was still up in material, had a whole extra bishop. And in a fair game he should have run out of time first and lost. 

Guys, what in the world happened? I lost a game I should have won. This also happened to me in another game.

Its because of lag. your opponent had a lot of lag so that is why extra time was added

The more lag you have, the more time you get over your opponent

Because of lag the time you see on your screen isn't necessarily the time that your opponant actually has. There was a thread awhile back that gave a good technical explaination of this, but crap if I can find it now.

Ok, I've played a lot more games now, and it keeps happening every other game. It keeps adding 10 seconds, even when there is a green box right next to my opponent's time. And I have about a half second lag too. 

If this is just the way chess.com is, they better fix it or it is messed up. 

Guys, correct me if I'm wrong, but a green box means the other person has a great connection, right?

The green box means there is a strong connection, but it does not mean there is no lag. You can count on some degree of lag no matter how strong one's connection may be. That's just the nature of the internet.

Ok, thanks for the info guys. 

You can see your opponent's lag but not your own. In your browser the clock is counting down normally, then it receives the info that your opponent actually moved two, five, ten seconds ago. So it adds that time back to their clock. Your computer can see your own move instantly so it looks like you never get time added.

ive just played a 10/15 game and i was trying to time my opponent out as i had 5 minutes remaining but he only had 1 but he was up on material and chasing down my king and pawns. every move he played it gave him an extra 10 seconds making it impossible to time out as his time was going up. is this the same reason of lag?

he was probably using hacks

That's what that time control setting means.

https://www.chess.com/terms/chess-time-controls

Looks like you were playing 15|10. That means that 10 seconds are added to a player's clock after they make each move.

Good

how about losing more time, like a second every move, right after taking turn?

Sound like a lot of lag between you and the site.

For things you can control take a look through the following:
https://support.chess.com/article/4720-online-chess-performance-optimizations

https://support.chess.com/article/213-how-do-i-fix-my-disconnect-lag-issues

I am having the same issue on the 1 minute games. Opponent is down to 1 sec. I have 9. Suddenly, the opponent has 10 secs and I lose on time. This didn't start happening until a month or so ago. Very disappointing. You play based on the time you think your opponent. I see the "lag" comments but after so many years, thus has cropp

* this has cropped up. I hope they can find a solution.

Nope, YOU have to find a solution: Either get a fast internet connection, or else stop playing 1 min games.

I believe with chess.com bullet if your opponent has high lag and you don't, for both it feels like the other player has some extra time when really there's this transit time.
Sometimes it feels like I'm splitting this difference with them, other times not. I say this because I will be making moves and continually getting these "corrections" to their clock when I get their move, and in other cases this doesn't happen so much.
another casual lichess w