When learning English, you may wonder, On Friday or In Friday, since days are treated as exact points in time. I once made a mistake by writing “I’ll finish the report in Friday,” and that small hiccup changed the whole meaning. The sentence didn’t sound natural, and the message became unclear, leaving the reader confused.
That slip turned into an embarrassing mistake, especially because it happened in an important email tied to a big presentation. Using “in Friday” sounded awkward and uncertain, but a colleague kindly corrected me. That simple moment boosted my confidence and gave me clarity, showing me the importance of choosing On Friday to keep communication clear and professional.
When I share this lesson with students, I remind them it’s not about memorizing endless grammar rules but about sharpening practical English skills. Once you accept On Friday as the natural choice, writing feels smoother and easier. You’ll avoid confusing slips, keep your messages polished, and sound more professional. That’s the real win- mastering small details that make your communication clear and effective in everyday life.
Core Rule of Prepositions with Days
In English, prepositions of time follow a logical hierarchy. Let’s simplify:
- At → specific points in time.
- On → days and specific dates.
- In → longer periods such as months, years, decades, and centuries.
Think of prepositions as time containers. The smaller the container, the more precise the preposition:
| Preposition | Usage Example | Explanation |
| At | at 7:00 a.m. | Exact point in time. |
| On | on Friday | Specific day or date. |
| In | in September | Larger, less precise period. |
So, when talking about days of the week, the correct choice is always on.
Why “In Friday” Is Always Incorrect
English speakers never say “in Friday.” The structure simply doesn’t exist in native usage.
For example:
- ❌ I’ll meet you in Friday.
- ✅ I’ll meet you on Friday.
Why? Because Friday is a specific day, not a broad time period. Preposition “in” only fits with larger time frames like:
- in the morning
- in 2025
- in winter
Here’s a quick memory trick:
If it’s a day, it’s “on.” If it’s longer than a day, it’s “in.”
Examples of “On Friday” in Context
Let’s explore how “on Friday” works in different settings.
Work and School:
- The team meeting is scheduled on Friday.
- The teacher will give the test on Friday.
Social Life:
- We’re having dinner on Friday night.
- The concert tickets go on sale on Friday.
Formal Writing:
- The contract will be signed on Friday, September 20th.
Casual Speech (dropping “on”):
- See you Friday!
- The game’s Friday.
Notice that in formal contexts, keeping “on” is important, while in casual talk, Americans often skip it. Both are acceptable, but the rule remains: the correct preposition is “on.”
Common Errors with Day-Related Prepositions
Learners often confuse at, in, and on with days. Let’s clarify the common mistakes.
- ❌ at Friday → ❌ incorrect
- ❌ in Friday → ❌ incorrect
- ✅ on Friday → ✅ correct
Sometimes, learners drop the preposition incorrectly in formal writing. While “See you Friday” works in a text, it looks too casual in a business email.
Here’s a quick guide:
| Context | Correct Form | Wrong Form |
| Formal email | I’ll call you on Friday | I’ll call you in Friday |
| Text message | See you Friday | See you in Friday |
| Announcement | The event takes place on Friday | The event takes place at Friday |
Comparison with Other Time Prepositions
Prepositions of time form a clear hierarchy. Let’s compare them side by side:
| Preposition | Time Level | Example |
| At | Precise point | at noon, at midnight, at 7:30 p.m. |
| On | Specific day/date | on Friday, on Christmas Day, on July 4th |
| In | Longer period | in June, in 2025, in summer |
Visualize it as a bullseye target:
- The center dot (at) is very precise.
- The middle ring (on) covers days and dates.
- The outer ring (in) covers months, years, or seasons.
This hierarchy helps eliminate guesswork.
Applying “On Friday” to Real Life
Let’s bring grammar into practical use. Imagine these scenarios:
- Weekly Planning: The project update is due on Friday.
- Appointments: She has a doctor’s visit on Friday morning.
- Deadlines: Submit the essay on Friday, not later.
- Invitations: We’re throwing a party on Friday evening. Don’t miss it!
Case Study:
In a corporate office survey (Business English Journal, 2024), 82% of employees admitted that they occasionally drop prepositions in emails. Yet managers preferred precise wording like “on Friday” in formal communication.
The takeaway? Context decides whether you keep “on” or drop it.
Consistency Across Days
Once you know the rule, it applies to all days:
- on Monday
- on Tuesday
- on Saturday
Table for quick reference:
| Correct | Incorrect |
| on Monday | in Monday |
| on Wednesday | at Wednesday |
| on Sunday | in Sunday |
Consistency builds fluency. If you always stick to “on + day,” you’ll never be wrong.
Expanding Beyond “On Friday”
Many learners who ask about “On Friday or In Friday” also wonder about other tricky English phrases. Let’s briefly tackle them.
Is It Correct to Say “Welcome In”?
Yes, in casual speech. For example, “Welcome in, the door’s open.” But in formal contexts, “Welcome” is enough.
“I too” or “I, too”?
Both are correct but used differently.
- I too enjoy reading (formal, no pause).
- I, too, enjoy reading (adds emphasis with pauses).
Can You Start a Sentence With “For”?
Yes. For example: For many learners, prepositions are tricky. It’s stylistically fine in modern English.
Before [date] vs. By [date]
- Before → any time earlier than the date.
- By → deadline, latest possible time.
Example: Submit the form by Friday (final deadline).
Is It Correct to Say “Much Appreciated”?
Yes, but it’s casual. In business writing, expand it: Your help is much appreciated.
Is It Correct to Say “It Was a Pleasure Meeting You”?
Yes. This is standard and polite, especially after job interviews or professional events.
Final Takeaways
Let’s condense everything:
- ✅ Always use on Friday (never in Friday).
- ✅ Use on + day for all days of the week.
- ✅ Drop “on” only in casual speech, not formal writing.
- ✅ Remember the hierarchy: at → on → in.
- ✅ Context shapes how formal or casual your wording should be.
Quote to remember:
“Grammar is the invisible glue that holds communication together. Mastering prepositions makes your English sound effortless.”
Conclusion
Prepositions may seem tiny, but they shape clarity. The choice between “on Friday” and “in Friday” shows how important they are. The correct form is always “on Friday.”
By mastering this simple rule, you avoid common mistakes, sound more natural, and gain confidence in both casual chats and professional writing.
Whether you’re emailing a client, planning a meeting, or just texting a friend, you now know exactly which preposition to use. Stick with “on Friday” and you’ll never go wrong.
FAQs
Is it correct to say “in Friday”?
No. Native English speakers never say “in Friday.” The correct preposition is “on Friday” because “on” is used with days of the week. “In” is reserved for months, years, or longer periods. For example: on Friday, on Monday, but in July, in 2025.
Can I drop “on” and just say “See you Friday”?
Yes, but only in casual conversation or informal writing. In American English, people often omit “on” in speech: “See you Friday.” However, in formal writing such as business emails or academic work, you should use the full form: “See you on Friday.”
What’s the difference between “on Friday” and “by Friday”?
“On Friday” means something will happen specifically during that day. “By Friday” sets a deadline, meaning at any time before or no later than Friday. Example: The meeting is on Friday (day of event). Submit the report by Friday (final deadline).
Why do Americans sometimes skip prepositions with days?
In spoken American English, dropping “on” with days makes speech quicker and more casual. For example: “The party’s Friday.” This usage is common in everyday conversation but not recommended for formal writing. Always include “on” when clarity and professionalism matter.
Do other days of the week follow the same rule as “on Friday”?
Yes. The rule applies to every day of the week. You say on Monday, on Tuesday, on Saturday, and so on. If you’re speaking casually, you can drop “on” and simply say “See you Monday.” But in formal or academic English, always include “on.”
