Like the tittle says, how often do you replay games?

And I'm not talking about multiplayer games or games that have online matches, I mean is how often do you play a game for it's single player. 

I personally used to re-play games all the time. I have beaten multiple N64, GC and Wii games countless times, Paper Mario like 7 times, TTYD like 10 times, Wind Waker like 6 times, Fire Emblem: Radiant Dawn like 500000 times (I honestly lost count) and many more. But now that I have a full time time a job and all that jazz, I really only have time to play the game once and very rarely come back to it. The game has to be extremely good for me to replay its single player, at the top of head, as of recent, the only games I have replayed are Fire Emblem: Awakening, Bioshock Infinite, A Link Between Worlds and Portal 2; and even then I have only beaten each twice. Growing up sucks I guess.

The only game I keep replaying all the time is Ocarina of Time, I made a promise to myself that I was gonna beat that game at least once a year until the day I die, and so far so good.

Not often. I usually play a game for an hour here and there totaling up to 3 hours majority of the time. I still have unopened games!
What I can connect with you though is that Zelda high.

Just beat SM64 for the tenth million time 2 days ago.

Whenever they are re-released, like HD collections. Otherwise rarely, too many other games to play. After all I have a massive catalogue of classics to catch up on and theres always lots of new games coming out.

Depends on the game really. I usually replay through games with alternate endings or outcomes.
My favorite game is Fallout 3, and I've completed that game as well as the DLCs 10 times or more. I also go back to playing through it from a certain point every now and then and I do the same with The Elder Scrolls V: Skyrim. I replay Resident Evil 4 a lot to try out the different difficulties. I play through Portal 2 a lot, and I've gone back and completed Half-Life 2 and episodes 1 & 2 as well.
But there are so many I'll go back to again after a year or two gap from completing them last. Like I feel I'll go back and complete the Assassin's Creed series again eventually.

Depends on how much I like a game. Currently on my fourth play through of DR3 and will replay it at least a couple more times since I haven't beaten it in Nightmare mode yet.

Pretty often I guess. The one I did the most was Sonic Chronicles: The Dark Brotherhood.

With games that have multiple endings, I usually only get 1 ending and watch the rest on youtube. The only exceptions for me were 999 and Virtue's Last Reward, but that's probably because 1) the story is freaking amazing and 2) you can skip the text and parts you already done.

Heh. Well, I just always get so involved with the RP side of things, as well as the over-all experience. Some outcomes, I do rather watch them on YouTube, but most I end up playing through them myself.

Often, though it involves an explanation. I only keep games that I like, or in some cases feel obligated to keep(Final Fantasy 13,) or games that I thought I might like but have yet to play. If I like the game and I don't own it, I'll eventually purchase it. Between all the systems I own, including portable, I have over 650 and that's not counting the digital games I own on Steam and GOG.

If I don't like a game and I'm certain I'll never replay it, I'll sell it. So by I replay games often, I mean as often as I can considering how much I own. Some games get more priority over others. I almost regularly replay my favorite classic platformers like the Mega Man series, Castlevania, and Ninja Gaiden 2, and RPGs that I replay include, Final Fantasy, and Brigandine, both which I've probably replayed just as much as said platformers I listed earlier. Other games I go through when I'm not playing anything else.

Problem is, by replaying these games instead of working on newer games or my backlog, my backlog is only getting bigger. But I feel the need to play games I like after playing something I really didn't like at all without playing something new that I also might not enjoy.