Determining the gender of a young parakeet can be difficult. However, once the parakeet has reached sexual maturity (six months to a year), there are a few ways to determine parakeet gender fairly accurately.
Look at your parakeet's cere (the colored band at the top of the parakeet's beak where the nostrils are). The ceres of sexually mature males are usually blue or purple, while female ceres are typically a pinkish-tan or brown.
Observe your parakeet's behavior. Females tend to be more aggressive, and typically gnaw and try to nest. Males will sing and learn to whistle and talk more readily. Often, males are more physically active than females as well.
Check your parakeet's cage regularly for eggs once the bird has reached maturity, especially if it also has a pink-to-brown colored cere. Eggs obviously confirm that you have a female.
Contact your veterinarian and ask about DNA testing if you want to be positive about the gender of your parakeet.