The author added that she is unlikely to don a costume from the popular books to mark the milestone, saying she looks "embarrassed" when given a prop and asked to pose for a picture.
Rowling had the idea for Harry Potter while on a delayed train to London King's Cross in 1990, and over the next five years began to plan out the books in the series.
The first book, Harry Potter And The Philosopher's Stone, was published in 1997.
Since then, more than 500 million copies of the books have been sold worldwide in over 80 languages, and the beloved character has made it to the silver screen as well as being transformed into a theatre show.
Speaking to Rowling on BBC Radio Two on Saturday, presenter Claudia Winkleman asked whether the writer might put on a Gryffindor gown and "celebrate big time" or have cheese on toast and watch a box set for the anniversary.
Laughing, Rowling replied: "Now you've reminded me of that, I think I probably will have cheese on toast, but I might open a bottle champagne and have some champagne with my cheese on toast.
"I probably won't dress up. That brings me back to, in the early days of Potter, every photographer wanted me to put on a witch's hat and it just drove me crazy."
The world-famous writer said she is "very bad" at having her photograph taken.
She said: "I'm particularly bad if someone gives me a prop to play with, or a hat to put on. I just look embarrassed and awful."
Rowling's latest book, The Christmas Pig, inspired by her son's love for a toy pig he had as a child, is due out next week.
She is hopeful it will "lead to interesting conversations between adults and children", adding that it deals with "some quite weighty themes".
During the interview, in which she also answered questions from members of the public, she was asked which was the one book she wished she had written.
Choosing A Christmas Carol by Charles Dickens, she described it as "utter writing perfection".