Someday and some day can both be correct, but they are not always used in the same way. Someday is normally written as one word when it means “at an unknown time in the future.” For example, “I hope to travel abroad someday.” Some day is written as two words when some directly describes a particular or unspecified day, as in “We need to choose some day next week.”
The confusion exists because the two forms sound alike and their meanings can overlap. This guide explains the difference between someday and some day, their history, British and American usage, common mistakes, and practical examples so you can choose the right form confidently.
Quick Answer
The correct choice depends on what you mean.
Someday is an adverb meaning at an unknown or unspecified time in the future.
I hope to visit Japan someday.
She wants to become a writer someday.
We will meet again someday.
Some day is a two-word phrase in which some modifies the noun day. It usually refers to an unspecified day or a particular day being considered.
We should meet on some day next week.
On some day in the future, people may live on Mars.
A simple rule is:
| Form | Meaning | Example |
|---|---|---|
| someday | At an unknown time in the future | I will finish the book someday. |
| some day | An unspecified or particular day | We can meet some day next week. |
In ordinary writing, when you mean “at some unknown time in the future,” someday is usually the best choice. Cambridge defines someday as referring to a future time that is not known or stated. (Cambridge Dictionary)
The Origin of Someday or Some Day
The difference between someday and some day comes from the way English gradually combines frequently used word groups.
The word some comes from Old English sum, meaning an unspecified person, thing, amount, or number. Day comes from Old English dæg, referring to a period of daylight or a 24-hour period.
English has a long history of turning frequently used combinations into single words. This process can be seen in words such as someone, somebody, and somewhere. Someday developed in the same general pattern.
Today, someday functions as an established adverb. It expresses an indefinite point in the future:
I would like to own a house someday.
By contrast, some day keeps the two words separate when some functions normally as a determiner describing the noun day.
This distinction is useful because the spelling reflects the grammatical role:
- Someday = one-word adverb
- Some day = determiner + noun
That is why both forms can appear in dictionaries and grammatically correct writing.
British English vs American English Spelling
There is no major British-versus-American spelling difference for someday. Both varieties recognize someday as a standard one-word adverb.
The same applies to some day when the two-word construction is grammatically appropriate.
| Usage | British English | American English | Example |
|---|---|---|---|
| Future time, unknown | someday | someday | I will visit someday. |
| Unspecified day | some day | some day | We can meet some day next week. |
| Particular emphasis on “day” | some day | some day | Some day in May would work. |
| Formal writing | Both possible | Both possible | Choose according to meaning. |
So, unlike differences such as colour/color or organise/organize, this is primarily a meaning and grammar distinction, not a national spelling distinction.
For everyday English, use someday when you mean an unknown future time. Cambridge lists the same basic meaning for British and American English. (Cambridge Dictionary)
Which Spelling Should You Use?
Use someday in most sentences where you are talking about a future event without giving a specific time.
I hope to learn another language someday.
They may return someday.
Someday, I want to write a book.
Use some day when some describes the noun day.
We need to select some day for the meeting.
On some day next month, we will visit the museum.
A useful test is to replace the expression with “at an unknown time in the future.”
If the sentence still makes sense, someday is probably correct:
I want to travel there someday.
→ I want to travel there at an unknown time in the future.
For writers in the United States, United Kingdom, Canada, Australia, and other English-speaking regions, the same basic rule works. You do not need a different spelling simply because your audience uses British or American English.
Common Mistakes with Someday or Some Day
1. Using “some day” when you mean “eventually”
Incorrect or less natural:
I want to become successful some day.
Better:
I want to become successful someday.
Here, the meaning is “at some unknown point in the future,” so the one-word adverb is appropriate.
2. Assuming “some day” is always wrong
It is not.
We need to find some day when everyone is available.
Here, some directly modifies day, so keeping the words separate is natural.
3. Confusing “someday” with “sometime”
These words are related but not identical.
Someday specifically points to an unspecified future day or time.
Sometime can refer to an unspecified time in the past or future.
I hope we meet someday.
We met sometime last year.
Cambridge similarly distinguishes sometime as an unknown or unstated time in the past or future. (Cambridge Dictionary)
4. Confusing “someday” with “sometimes”
Sometimes means occasionally or on some occasions.
I sometimes work late.
Someday means at an unspecified time in the future.
I will retire someday.
These are completely different meanings. (Cambridge Dictionary)
Someday or Some Day in Everyday Examples
In emails
I hope we can work together someday.
This is natural when referring to an indefinite future opportunity.
If you are discussing scheduling:
We can arrange the meeting on some day next week.
In news writing
The technology could become widely available someday.
Here, the writer does not identify a particular date.
In social media
I hope I can visit this place someday!
This is a common conversational use because the exact future time is unknown.
In formal writing
The policy may someday require further revision.
The one-word form works naturally in professional writing when it functions as an adverb.
With “one day”
One day is also correct:
One day, I will achieve my goal.
The phrase can mean “at some point in the future,” much like someday. Cambridge lists one/some day as an expression meaning at some time in the future. (Cambridge Dictionary)
Someday or Some Day – Comparison Table
| Feature | Someday | Some day |
|---|---|---|
| Number of words | One | Two |
| Main function | Adverb | Determiner + noun |
| Main meaning | At an unknown future time | An unspecified day |
| Common use | Future hopes or plans | Referring to a day |
| Example | I will visit someday. | We can meet some day next week. |
| British English | Correct | Correct when meaning requires it |
| American English | Correct | Correct when meaning requires it |
| Best shortcut | “Eventually” | “An unspecified day” |
The most important point is that someday is not simply a “correct” version of some day in every sentence. The two forms perform different grammatical jobs.
Someday or Some Day – Google Trends & Usage Data
Google Trends is useful for examining search interest, but it should not be treated as a dictionary or a direct measure of how often a word is used in normal writing. Google explains that Trends shows search-interest patterns and allows comparisons across places and time periods. (Google Trends)
For this keyword, search intent is likely to come from people who are unsure whether someday should be written as one word or two. That makes the query particularly relevant to grammar, spelling, and proofreading searches.
The one-word form also has strong dictionary recognition: Cambridge lists someday as an adverb meaning an unknown or unstated future time and provides examples from English-language corpora. (Cambridge Dictionary)
Because Google Trends does not provide a simple universal “correctness score,” writers should not choose a spelling solely because one form appears more frequently in search results. Meaning and grammatical function are the better guides.
FAQs About Someday or Some Day
1. Is “someday” one word or two?
Someday is one word when it means “at an unknown time in the future.”
I will visit you someday.
2. Is “some day” also correct?
Yes. Some day is correct when some describes the noun day.
We will choose some day next week.
3. Is “someday” grammatically correct?
Yes. Someday is a standard English adverb.
4. Should I write “some day” or “someday” in formal writing?
Use someday when you mean an unspecified future time. Use some day when the phrase specifically describes a day.
5. Is “someday” American English only?
No. Someday is used in both British and American English.
6. What is the difference between “someday” and “sometimes”?
Someday refers to an unspecified future time. Sometimes means occasionally.
I will travel there someday.
I sometimes travel for work.
7. What is the difference between “someday” and “sometime”?
Someday generally points to an unspecified future time, while sometime can refer to an unspecified time in either the past or future. (Cambridge Dictionary)
8. Is “one day” the same as “someday”?
They can have the same meaning when talking about an unspecified future time.
Someday, I will own a business.
One day, I will own a business.
9. Can “someday” be used at the beginning of a sentence?
Yes.
Someday, people may find a solution.
10. Can “someday” be used in professional writing?
Yes. It is a standard word and can be used in both everyday and professional English when the meaning is appropriate.
11. Is “some day soon” correct?
Yes. Here, some day can remain separate because some modifies day.
We should meet some day soon.
However, someday soon is also a natural construction when the meaning is “at some future time soon.”
12. What is an easy way to remember the difference?
Remember: someday = sometime in the future. If you are talking about an actual or unspecified day, use some day.
Conclusion
Someday is the correct one-word form when you mean “at an unknown time in the future,” while some day is used when some directly describes the noun day. The practical rule is simple: if you can replace the word with “eventually” or “at some future time,” choose someday. If you are referring to an unspecified day, keep the words separate.
This distinction works in both British and American English. For more useful spelling and grammar guidance, consider linking this article internally to a related post about sometime vs sometimes, since these words are commonly confused as well.
