In a Day vs. On a Day

In a day means in the duration of a day (24 hours). The expression is used when an event or action happens within the duration of a day. On a day means on such a day. The phrase is used to convey that the day in question is different from a typical day.

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In a day

Here’s an example of in a day:

Suzy finished the project in a day.

In the example above, the subject of the sentence, Suzy, completes her project within the duration of one day. In other words, she completes her project within 24 hours.

More example sentences

On average, I drink about eight glasses of water in a day to stay hydrated.
The bakery produces hundreds of fresh pastries in a day to meet the high demand from customers.
I can usually complete my work tasks in a day if I stay focused and avoid distractions.
In a day, the sun rises in the east and sets in the west, providing us with daylight.
The factory can manufacture thousands of widgets in a day with its automated production line.
It's amazing how much progress you can make in a day when you're motivated and determined.
The delivery service promises to deliver packages to your doorstep in a day or less.
I like to set aside at least an hour for reading in a day to relax and unwind.
In a day, our planet Earth completes one full rotation on its axis.
The emergency room at the hospital sees a constant stream of patients, with dozens being treated in a day.

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On a day

On a day is used when the day in question is different from a typical day. It’s a day that has a quality that sets it apart from other days.

I can’t believe Nate is going to propose to Zoe on a day like this!

In the example above, Nate is going to ask his partner to marry him on a day that is not suitable for a proposal. This day in question is different than other days that would be socially acceptable for a proposal.

More example sentences

On a day like today, the sun is shining brightly.
On a day of celebration, we gathered with friends and family.
On a day of mourning, we paid our respects to the departed.
On a day in December, snowflakes gently fell from the sky.
On a day of reckoning, the truth will be revealed.
On a day of discovery, we stumbled upon hidden treasure.
On a day of chaos, it's best to stay calm and composed.
On a day in history, a significant event occurred.
On a day of reflection, I pondered life's mysteries.
On a day of anticipation, we eagerly awaited the arrival of our guests.

On the day

On the day means on a certain, specific day. It is used when denoting a particular day.

James resigned on the day of the company-wide pay raise.

Here, we can see that James quit his job on the specific day that the company issued a pay raise for all its employees. What timing!

More example sentences

On the day of the wedding, the bride looked absolutely radiant in her gown.
We met some old friends on the day of our high school reunion.
On the day of the big game, the stadium was packed with cheering fans.
He finally received his diploma on the day of his college graduation.
On the day of the interview, she wore her best suit to make a good impression.
On the day of the presentation, I felt a mixture of nervousness and excitement.
They exchanged heartfelt vows on the day of their anniversary.
On the day of the festival, the streets were filled with colorful decorations.
On the day of the exam, she reviewed her notes one last time before entering the classroom.
We lit candles in remembrance on the day of the memorial service.

Practice questions

We’ve prepared some practice questions you can try out to augment your understanding of the three phrases. You can find the answers at the bottom of this article.

She gave birth in a day/on a day/on the day of her wedding anniversary.
Wayne swiftly built a tree house in his backyard in a day/on a day/on the day.
Why is Paola trying to wash her car in a day/on a day/on the day when it’s raining this much?
Our manager wanted the marketing proposal to be finished in a day/on a day/on the day so it could be presented the very next day.
Justine ate the whole cake by herself in a day/on a day/on the day.
I’m glad I started my first job in a day/on a day/on the day like this; it’s perfectly sunny with not a single cloud in the sky.
Grace did not want to go to the amusement park in a day/on a day/on the day of her father’s death anniversary.
Ulysses was excited he got a bonus in a day/on a day/on the day before his daughter’s birthday.
Why would you do a picnic in the park in a day/on a day/on the day this hot?
Did you finish the summer assignment all in a day/on a day/on the day?

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