Check the freshness of your egg by placing in a bowl of cold water. If it sinks, it's still good, if it floats discard

Eggs go bad because the air permeates the shell and oxidises the proteins. To prevent this, take your fresh egg and smear generously in cooking oil, or dip into the deep fat fryer while the oil is cold. Let the excess drain away through the basket. The film of oil on the shell will stop the air permeation

Finally, return to the egg box. Believe it or not, if done correctly, the egg should be fine for at least a year, but check for freshness using the bowl trick before use