Is Re Capitalized In A Letter? | Subject Line Rule

When people ask this, they’re usually talking about the line near the top of a letter that names the topic. In that spot, the usual form is Re: with a capital R and a colon. A line like Re: Account Update looks normal to most readers and keeps the purpose plain from the first glance.

The mix-up starts because re can do more than one job. It can label the subject of a letter. It can appear in the legal phrase In re. It can also show up in older prose as a word meaning “about.” Once you split those uses apart, the rule gets simple.

Is Re Capitalized In A Letter? The Usual Rule

Use Re: with a capital R when it starts a subject or reference line in a business letter, formal note, or email. That is the form most office readers expect. It looks tidy, and it signals that the words after it name the matter the letter is about.

You do not need to capitalize plain re when it sits inside a sentence. If you wrote, “I’m writing re the lease renewal,” the word would stay lowercase. That phrasing sounds old-fashioned to many readers, so most people now write “about” or “regarding” instead.

• Use Re: for a subject or reference line.
• Use Subject: if you want a plainer label.
• Use lowercase re only as a normal word in a sentence.
• Use In re in legal matter names, not as a regular business-letter label.

What “Re:” Is Doing On The Page

On a letter, Re: acts like a signpost. It tells the reader, “This is the matter I’m writing about.” That makes it handy for letters tied to one case, one invoice, one claim, one application, or one account. If the reader handles stacks of mail, that small line helps them sort the letter fast.

That does not mean every letter needs it. If your first line already states the topic in plain terms, a separate Re: line may feel like extra furniture. In a short personal letter, it can look stiff. In a formal complaint, legal notice, or claims letter, it still fits well.

Why The Rule Feels Fuzzy

Writers meet re in three places that look alike but act differently. A subject line uses Re:. Legal captions use In re. Old-school prose may use lowercase re to mean “about.” Those forms overlap on the page, so people often treat them as one rule when they are not.

There’s also a modern shift in email. Many people drop Re: and go straight to a plain subject line. That is one reason the label can feel dated in some workplaces. Still, dated is not the same as wrong. If your office, school, or firm still uses it, capitalizing the R is the clean choice.

Capitalizing Re In A Letter Subject Line

A business-letter handout from the University of Arkansas shows a reference line such as “RE: Invoice 1234”. That matches the form many readers know: capital R, lowercase e, then a colon. You can also write the topic after it in title case or sentence case, as long as you stay consistent.

If you’re writing email, plain wording still wins. Federal guidance from Section 508 on email messages says the subject and body should state the purpose clearly and concisely. So even when Re: is fine, the line after it should stay brief and specific.

Use this quick test: if the reader should know the topic before reading the first paragraph, a subject line can help. If the topic is already obvious from context, you can skip it and let the opening sentence do the work.

Situation	Best Form	Sample Line
Invoice dispute	Re:	Re: Invoice 1234
Insurance claim letter	Re:	Re: Claim No. 78451
Job application letter	Subject: or Re:	Subject: Application For Staff Writer
School appeal letter	Re:	Re: Grade Appeal For History 201
Customer complaint	Re:	Re: Damaged Order #5528
Short personal note	No label	Start with the opening sentence
Formal internal memo-style letter	Subject:	Subject: Budget Review Meeting
Legal matter heading	In re	In re Estate Of Maria Lee

Where To Put The Line

In a printed business letter, the subject or reference line usually sits after the recipient block and before the salutation. That placement gives the reader the topic before the greeting. If you use both a subject line and a reference line, keep them short so the top of the page does not get crowded.

In email, the same idea moves to the subject field. You usually would not type Re: inside the body unless you are pasting a formal letter format into the message. Many mail apps add Re: on replies by default, so adding it by hand can look clunky.

Common Mistakes That Make The Line Look Off

The first slip is writing re: in all lowercase. That can look unfinished in a formal letter. The second is shouting with RE: in full caps when your office does not use caps elsewhere. The third is forgetting the colon. Without the colon, the label loses its clean stop before the topic starts.

Another slip is writing a vague topic after the label. Re: Question tells the reader almost nothing. Re: Return Request For Order 5528 gives them a fileable, searchable subject. Short is good. Foggy is not.

When You Should Not Use “Re:”

Skip it when the letter is personal, warm, or already clear from the first sentence. A thank-you note does not need a subject line. A brief follow-up email often works better with a direct subject such as “Tuesday Meeting Notes” than with “Re: Tuesday Meeting Notes.”

Also skip it when your house style already favors plain-English labels. Many offices now use Subject: because it is clear to everyone at once. If you work in a legal setting, the house style may lean the other way and keep Re: or In re in routine use.

For legal wording, Cornell Law’s Wex entry on “in re” defines it as “in the matter of.” That phrase belongs to case names and legal captions. It is not the same thing as the everyday Re: line in a business letter, while both point to the matter at hand.

Form	Use It Here	Example
Re:	Formal subject or reference line	Re: Lease Renewal
re	Inside a sentence, old-style “about” sense	I’m writing re the lease renewal.
RE:	Only if your office style uses full caps	RE: POLICY UPDATE
In re	Legal caption or matter name	In re Estate Of Maria Lee
Subject:	Plain-English label	Subject: Lease Renewal

How To Make The Line Look Polished

If you decide to use Re:, keep the rest of the line clean. Name the matter, file number, or request in a few words. Put the most useful term first. That way the reader can scan it in one pass.

1. Write Re: with a capital R and a colon.
2. Add the exact topic right after it.
3. Use title case or sentence case and stick with one style.
4. Drop filler words, dates, and backstory unless they help identify the matter.
5. Let the first paragraph pick up the same topic without repeating the whole line word for word.

A clean subject line might look like this: Re: Refund Request For Order 5528. The first paragraph can then open with the facts, the date, and the action you want. That gives the reader a smooth path from label to message.

So, is Re capitalized in a letter? Yes, when it works as the subject label. Use Re: for the line at the top, keep plain re lowercase inside a sentence, and switch to Subject: or no label at all if that fits the letter better.