Continuity mistake: The first time John's alarm goes off at 0600, it is early moments of dawn. A little while later in the movie we see John being woken up by the puppy at 0600 and it is brighter, almost mid morning kind of light. (00:01:35 - 00:07:50)
Continuity mistake: At the start, the blood splatter on John's phone changes instantly between shots. (00:01:50)
Other mistake: When we see John's wife collapse in front of the bride, just as the camera cuts out of this little cut scene, the camera wobbles very noticeably. Almost as if someone had knocked it. (00:02:25)
Continuity mistake: Just when John Wick puts the bracelet on the night table next to the phone near the start of the film, the time changes all of a sudden from 8 to 10. (00:04:00)
Continuity mistake: When John first meets Marcus in the cemetery, John's umbrella changes from a standard 8 rib when lowering the coffin, then a 22 rib close up, then back to 8 ribs in a far shot of the two men shaking hands. (00:04:15 - 00:05:45)
Continuity mistake: John opens the envelope that comes with the dog and it's a standard pointy envelope flap. When the shot changes it's now a horizontal flap envelope. (00:06:50)
Continuity mistake: When John is going to bed with Daisy for the first time, the clock says 10:50. John puts a pillow on the floor and now the clock's showing 10:54. (00:08:30)
Continuity mistake: As John gets up in the night near the start, the clock reads 1:41. As he is physically getting out of bed it reads 10:00. (00:12:40)
Revealing mistake: Just as John grabs the dog after being attacked, the dog is added post production. This is identifiable as his little finger goes through the dog. (00:14:00)
Continuity mistake: John gets his nose broken by Iosef when attacked at home. However, when he buries the dog, there are no marks on his nose or face. (00:14:30)
Continuity mistake: After subduing one of the henchmen at his house, John sees another one come behind his staircase's side glass pane. He shoots the henchman, putting a bullet through the glass. The shot changes to him finishing the henchman, but when the shot goes back to the stairs seconds later, the bullet hole has disappeared from the glass. (00:29:55)
Character mistake: When he called for a dinner reservation for 12 at his home it should have been 13, as he put 13 men down. (00:32:05)
Suggested correction: Actually 14.
It's possible he simply miscounted in the heat of the moment. I'm not saying you're wrong was John doesn't seem like the type to make this sort of mistake but it could be let off as a character mistake rather than a movie mistake.
A character mistake is a valid movie mistake and this entry is listed as such.
Continuity mistake: Just after his dinner reservation, we see John driving over a bridge. In the aerial view we can see several cars in front of him on the bridge. However from the shot inside the car, there are no cars in front of him. (00:34:30)
Audio problem: Winston asks John if he has returned to the fold. In this shot, the camera is over the shoulder (of Winston) and Winston's audio is overdubbed. (00:40:25)
Other mistake: When John is talking to the club bouncer, John says that he lost weight, to which he replies (in Russian) "Twenty kilograms." The translation says "over sixty pounds," but 20 kilograms is just over 44 pounds. (00:46:30)
Suggested correction: Maybe he's actually saying "Over 20 kilograms" in Russian. If you calculate the other way 60lbs is just over 27kgs.
Logically that doesn't make a lot of sense since the mistake is saying the translation says "over 60 pounds", so we have to assume by 20 he means over 27.6. Why not just just say "over 27 kg"? And you appear to just be guessing that maybe he says "over 20 kg" in Russian.
Watching it literally right now... he absolutely says "20 Killogramma".
Continuity mistake: In the red circle, John stabs a guy in the shoulder before shooting him. When he shoots him however the knife has disappeared. (00:48:40)
Continuity mistake: John stabs a guy below the chin and we see his hand get blood on it in a closeup. Next shot he pulls the knife against another guy, and his hand and shirt sleeve are perfectly clean. (00:49:30)
Continuity mistake: John is thrown off the balcony in the red circle. When he lands, he doesn't have a gun in his belt at the back, but he then magically pulls one out a few seconds later. (00:50:30)
Continuity mistake: The bullet hole from Marcus' shot at John's pillow disappears when he rolls over the bed. (00:55:20)
Continuity mistake: The holes that Ms. Perkins puts into the glass above John's bed keep disappearing and reappearing. This is not to be confused with the extra bullet hole mistake already listed. (00:55:50)
