J.K.Rowling - Official Site

Birthdays

On July 30, 2004 the Wizard of the Month calendar changed to say Happy Birthday to Neville Longbottom. The next day, July 31st, it (of course) said Happy Birthday Harry Potter. These were the first birthdays displayed and started a year of anticipation as we watched the calendar for more birthdates! Over the course of the next year 19 birthdates were announced (20 if you count both Weasley twins), the last new one being Dobby on June 28, 2005.
Since then they have all simply repeated.
The birthday greetings appear automatically at midnight UK time and remain for 24 hours.

• July 30 = Neville Longbottom
• July 31= Harry Potter



• August 11 = Ginny Weasley
• August 22 = Percy Weasley



• September 19 = Hermione Granger



• October 4 = Minerva McGonagall
• October 17 = Filius Flitwick
• October 30 = Molly Weasley



• November 29 = Bill Weasley



• December 6 = Hagrid
• December 12 = Charlie Weasley



• January 9 = Severus Snape



• February 6 = Arthur Weasley



• March 1 = Ron Weasley
• March 10 = Remus Lupin



• April 1 = Fred and George Weasley



• May 15 = Pomona Sprout



• June 5 = Draco Malfoy
• June 28 = Dobby

Besides the birthdates, there is more canon information we can gather from these.

• We learned, by order of the dates, that Hermione was either the eldest of the trio, or almost a year younger. Jo later confirmed that Hermione was older in her FAQ answer to the question from the Open Letter to J.K. Rowling.
  
  
• We have confirmation of the first names of Filius Flitwick and Pomona Sprout, which we surmised from their Trading Cards, but had not yet confirmed. (Another question on the Open Letter to J.K. Rowling.)
  
  
• We also had more information on determining the ages of the elder Weasley brothers, Bill, Charlie and Percy; and the age difference between them (months and years).
  
  
• We can assume that House-elves are born and note the date, since Dobby has a birthday.