What is the significance of Ran's birthday? Ran's birthday is usually seen as something important in the anime and manga and is talked about a lot. Yet, throughout the entire series of 660+ episodes and 70+ volumes, it has never actually happened.

Why is Ran's birthday so important to the plot?
Officially, neither the birthday is revealed, nor has it really played a role in the plot.
However, Aoyama said in an interview, that there is an &quot;obstacle&quot; preventing him from revealing Ran's birth date, but since the birthday hasn't passed Ran is 16 right now&quot;
The interview, quoted from Detective Conan World's forum:

蘭の誕生日教えて！→差し支えあるので今は言えない。でもまだ誕生日来ていないので蘭は現在16歳。
Tell me about Ran's birthday! → Since there's an obstacle, I can't tell it for now. But since the birthday hasn't passed, Ran is 16 right now.

I think that a future volume will be about her birthday, so everything else would be wild speculation.