What is the difference in meaning between on the same day and in the same day. I thought that on the same day was the only one correct, but in the sixth episode of the eighth season of Friends Phoebe said in the same day. Here is the context:

Phoebe: He is sweet. He’s too sweet. He calls me all the time. (Mimicking him) "So did-did you get home from work okay?" "Did-did you get out of the shower okay?"

Monica: Just don’t pick up your phone.

Phoebe: Then he comes over! (Mimicking him) "I’m so worried about you." Uck! Be a man!

Monica: What? So now I’m not allowed to fire him?

Phoebe: You can’t fire him and dump him in the same day, he’ll kill himself.

Here is the video. It's at 1 minute and 40 seconds.

2 Answers 2


It depends if you are speaking about a "day" as a calendar date or a time period.

We always say "on" a particular date or weekday, for example:

  • it happens on Mondays
  • It's on the 4th of July

When we are speaking about a time period, we use "in" or "within", for example:

  • it happened twice in 24 hours
  • it happened twice within an hour

A "day" isn't necessarily a calendar date from midnight-midnight. It can be any 24-hour period. It can also refer to specific periods of time that are less than 24 hours, for example a working day may be just the hours you spend working.

In the example you give it might be that it refers to two incidents on the same calendar date, but the point of the statement is to express shock that the two things would happen so close together, within the confines of 24 hours. In this case, either "in" or "on" work fine.

As an example, if someone said "I once ate 12 burgers in a day", what is remarkable about that statement is that they ate the burgers in a 24-hour time period, not that they may have all been consumed on the same calendar date.


On the same day is the more usual but both can be correct. In the same day tends to used more in situations to describe events that require completion within the time period of one day. 'You can't lay the bricks, plaster the walls and paint the woodwork in the same day.'

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