Before answering this question you must first understand the difference between a human egg and an embryo. Eggs, or oocytes, are the female component of an embryo. An embryo is what is formed after a male sperm fertilizes the human egg. It is the embryo that will eventually turn into a fetus.
Most commonly your eggs will be turned into embryos within a couple of days following your retrieval. Those embryos will then be either transferred into the uterus of a surrogate, or frozen for future use. Once frozen, embryos can remain viable for many years, with cases of live birth resulting as long as 15 years after freezing!
The practice of freezing unfertilized human eggs for future use is not as well documented. The belief is that, like embryos, eggs will be able to remain viable for a number of years once frozen. Current research has highlighted frozen eggs being viable for up to 4 or 5 years, but the belief is that the eggs would maintain their usefulness as long as the freezing conditions remained consistent and optimal.
The cause for the lack of depth of knowledge in this topic is, in part, due to the fact that the practice of freezing human eggs is relatively new. While male sperm has been frozen and thawed for many decades, the first instances of human egg freezing only occurred in the 1980s. It was originally believed that the freezing of eggs would lead to an increase in chromosomal abnormalities. This original fear, observed in laboratory mice, caused researchers to postpone their studies.
Over recent decades, scientists have been able to dispel this concern and have witnessed healthy children born of embryos that were created using frozen eggs. The potential for egg freezing is only just beginning to be explored.