Kim Broughton found one of her hens - now renamed Ping Pong - had laid the round egg in her garden in Latchingdon, Essex, on February 17.
She decided to auction the egg in aid of the Cystic Fibrosis Trust after a friend's son died from the disease.
Broughton said she imagined the buyer was interested in preserving, rather than eating, the unusual egg.
The item, laid by a Buff Orpington hen - described as the "Scarlett Johansson of the chicken world" - attracted 64 bids on internet auction site eBay.
Broughton told the BBC that she had been tempted to cook and eat the egg before being told it was "one-in-a-billion".
She said: "I was literally about to crack it open to make a pancake when a mate saw the photo I put on Facebook and messaged me to say 'Don't do it!'
"Apparently somebody had sold one before for more than 90 pounds so I thought 'Great if I can sell if for that'.
"When it was at 20 pounds I thought 'Who'd pay that for an egg?' and then it went through the roof. It's unbelievable".
