We know that Harry's birthday is on July 31 because that is the same day as the break in at Gringotts. From the second book we know Nearly Headless Nick's 500th Death Day Party was on 10/31/1992. Doing the math, we know that Harry's 11th Birthday was 07/31/1991. In The Sorcerer's Stone, Harry says his birthday is on a Tuesday, the day after Dudley's favorite TV show (The Great Humberto). The mistake is that July 31, 1991 fell on a Wednesday, not a Tuesday like the book said.

When Hagrid brought Harry to Diagon Alley for the first time, Harry heard a woman say "Seventeen sickles an ounce for Dragon Liver. They're mad." But Hagrid told Harry that there were seventeen sickles in a galleon. So that would be like saying "100 pennies" instead of a dollar.

When Hagrid comes and gets Harry out of the little hut on the rock, they use the boat that the Dursleys used to get to the rock. So how do the Dursleys get off the rock?

Harry buys the book "One Thousand Magical Herbs and Fungi", but later in the book it says Harry looked up 'dittany' in "One Hundred Magical Herbs and Fungi."

Petunia Dursley says that Lily would "...come home every vacation with her pockets full of frogspawn, turning teacups into rats...," but according to ministry rules, this is illegal. If she did this in her muggle home she would most likely be expelled as Harry almost was.

Just a thought but... security for the Sorcerer’s Stone could have been much better. If three first-years can get to the stone than you can bet any fully trained wizard can do it. They could have just had a password that nobody but Dumbledore knew. Then he could tell Flamel if he had to use it than change the password right away.

In chapter 7, page 122, it says that Harry looked up at the Sorting Stool, there were only 3 people left to be sorted, Professor McGonagall calls the names of 4 more people instead. (Thanks to 'Mac'.)

'Ryan Richins' writes in to say: "In Book one (it said), Prof. McGonagall brings out a 4 legged chair with the sorting hat (to the sorting ceremony). In book four (it said) she brings out a 3-legged chair with the sorting hat. What happened to one of the legs?"

In Harry's letter from Hogwarts it says he could bring a cat, an owl, or a toad, but Ron still brings his rat, Scabbers.

In the first book when Hermione uses Petrificus Totalus on Neville, it says he "fell flat on his face, stiff as a board". Then, in the next paragraph, it says that Neville is looking up at Harry, Hermione and Ron in horror. -Submitted by mikedim

In Book 1, JK Rowling wrote that Ron was the knight in the giant chess set. However, it later said that he had to 'move ahead one' so the Queen could take him, opening the path for Harry and Hermione to checkmate the king. If he was a knight, he could only move 1) ahead one, sideways two, or 2) ahead two, sideways one, like an "L".

In the first book it said that by drinking the Elixir of Life it would make the drinker immortal, but later in the story Dumbledore says to Harry that the Flamel's had enough Elixir stored in them to set their affairs straight.. But, if by drinking the Elixir of Life makes you immortal then you would never die, ever. You can't just be immortal as long as you have a certain item, then that would mean you could die. You would be like Achilles, you could still die. Immortal means you can NEVER die.