The trees are green in scenes which supposedly take place in New York at Halloween and Christmas.
When Ted goes to apply for a job, the date is Friday, December 22. Near the end of the film when Ted's lawyer reads the court ruling, the ruling is dated Monday, January 23. If December 22 was a Friday (as it was in 1978), then it's impossible that January 23 fell on a Monday. In fact, the next time January 23 fell on a Monday wasn't until 1984.
Mr. Kramer's lawyer tells him that, if he wishes to appeal the decision granting custody to his ex-wife, his son would have to take the stand. On an appeal, no new evidence is called, and therefore the son would not be called as a witness.
The entire contention of Ted's custody of Billy rested on his ability to manage both his job and his parenting. Given that Ted was a successful advertising executive that had just landed the big airline account and was on his way to making partner, Ted could have easily afforded to hire a nanny to take care of Billy during the day, leaving no doubts to Ted's boss who exaggerated about Ted having to be available "24 hours a day, 7 days a week," which no advertising agency would ever demand of its associates.
The position of Phyllis' hands change several times when she is in the hallway naked.
Ted Kramer's lawyer tells him that his ex-wife will meet him and their son at "the Central Park Boat Pond," but when the meeting actually takes place it is at Literary Walk.
Ted is talking to his son after the first hearing to determine custody, and in so doing is speaking as if he grew up in the 1920's. Presumably, given Ted's age and the age when he was his son's (Billy) age, in the 1950's, Ted tells billy they didn't have television, Burger King or McDonalds, or diet soda, which is all false. Diet Rite Soda came out in the 1950's, the first McDonalds was in 1938 and they were prolific by the 1950's, Most affluent families had television in the 1950's and the first Burger King was in 1954. "Mostly we just listened to the radio," Ted tells Billy, which is more akin to living in the 1920's, so Ted's exaggerations are flagrant.
When Ted is first making French Toast, he picks up the egg in his right hand; when he shows it to Billy before breaking it, it's in his left hand; when the camera goes to closeup as he breaks the egg, it's back in his right hand. Dustin Hoffman's disheveled hair also changes wildly in that scene.
When Billy is waiting for Ted to fetch him after the birthday party, he sits on the chair with his left leg tucked under the right leg. In the next shot, his right leg is tucked under his left leg.
When Kramer takes Billy to his office in NYC he points out the Chrysler Building. Then they walk down the hall to his personal office and points out the UN Building. Therefore they were walking North. Kramer then points North of the UN Building and says that way down that way is Brooklyn. He was pointing at the Bronx, while Brooklyn would be South.
When Kramer is waiting to get his new job, a man with a red tie walks past him twice to speak to another person.
Ted's job interview takes place at 4pm on Friday, Dec.22nd (during the office Christmas party). The next scene has Ted and Billy visiting Ted's 'new' office. Ted tells Billy "It's Saturday, most people take the day off". Ted's office already has his name plate, pictures of Billy on the wall, and work assignments. This could only be true if a week had passed between the 2 scenes.
After Ted gets mad at Billy for eating ice cream instead of dinner, he carries him from the kitchen into the living room and the spoon in Billy's hand disappears.
Ted's job interview takes place at 4pm during the office Christmas party, but outside the office window Manhattan is bathed in bright mid-day sun.
When Billy wakes Ted the morning after the separation there is a yellow Trimline phone on the bedside table. Later that morning when Ted calls home from the office there is now a beige Princess style phone sitting on the bed.
Dustin Hoffman pours raw egg & milk mixture into the pan while making the french toast. Later the pan contents burn. The close-up shows it all as browning. After that close-up Hoffman drops the pan on the floor. The egg and milk mixture flies out, and it is raw again.
After Ted throws the wine glass at the wall, Joanna goes from having one hand at her jaw to having both hands.
While eating TV dinners for the first time w/ Billy, Ted's glass of Tab changes volume between camera shots.
Just after Ted & Billy finish "Don't let the bedbugs bite", Billy's hands with the stuffed animal changed from being next to his head to down by his chest.
When they meet over wine; the ashtray changes position on the table from when he walks in & is then sitting down.
When writing the 'pro's & con's' for his lawyer, a plate is at the upper left corner of the notepad, but it's not there in the distant shot.
When picking Billy up from the b-day party, Ted's hand goes down twice when he's given the 'goodie' bag.
Ted gets mad at Billy for eating ice cream instead of dinner, he lifts him from the chair and the ice cream on the spoon in Billy's hand is missing, while a second before Billy was about to have a giant bite.
When standing up after writing the pro's & con's for his lawyer, the pen changes position on the paper between shots.
After Ted drops Billy at school, Joanna's hand position on the window changes between shots.