The 'Twilight Saga' actress reaches the milestone age in February 2015 but hasn't made any plans to celebrate yet, and she admits she gets so tired of being asked about it, she is now expecting to just have a quiet night in.
Asked how she will celebrate turning 21, she said: "I have no idea what to do. It's been such a talked-about thing for so long, like, what are you gonna do for your birthday, that I think by the time it rolls around I'm just going to stay home with five friends and call it a day."
She also admitted she prefers crafting at home to partying in clubs.
She told the New York Post newspaper's Page Six column: "Pretty much every director I've ever worked for I've knit a scarf for."
Dakota is likely to spend her birthday with boyfriend Jamie Strachan, who she recently revealed she is "super happy" with and doesn't care about him being 13 years older.
She said: "I'm super happy. I think love is very important and it's really fun to have someone to experience things with. It makes everything a bit more special.
"People love who they love and you go with that. People get so stuck in rules for life. You go with what feels right."