Backup vs. Back Up
“Backup” is commonly a noun or adjective for support, a reserve, or an extra copy. “Back up” is the phrasal verb: you back up files, back up a claim, back up a vehicle, or traffic can back up.
Use “backup” for the thing: “Keep a backup.” Use “back up” for the action: “Back up your files.”
Key details
Choose the right form
| Role | Form | Example |
|---|---|---|
| noun/adjective | backup | a backup / backup copy |
| verb | back up | back up the files |
| phrasal verb with object pronoun | back it up | separate words |
Quick tests
Part-of-speech test
Are you naming the copy/thing, or describing the action of creating/supporting it?
If yes: Use “backup” for the noun/adjective and “back up” for the verb.
If no: Recast the sentence to identify whether the expression is acting as a thing/modifier or as a verb.
Caveat: Product names and fixed labels can have house spellings, but the ordinary noun-versus-phrasal-verb distinction remains useful.
Examples
Keep a backup of the database.
“Backup” is a noun.
Back up the database before upgrading.
“Back up” is the phrasal verb.
Please backup the database before upgrading.
Better: Please back up the database before upgrading.
In ordinary edited prose, the verb is written as two words.
Further guidance
Core difference
Use one-word “backup” mainly as a noun or adjective. Use two-word “back up” when it is a verb.
Fast Test
If you can put “to” before it—“to back up the files”—use two words. If you mean the extra copy itself—“a backup”—use one word.
Variant Boundary
Some dictionaries also record hyphenated “back-up” in particular noun/adjective contexts, especially in British/business usage, so house style can affect the non-verb spelling.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Backup — English meaning (opens in a new tab)Cambridge University Press · Noun and adjective uses of backup
- Back someone/something up — English meaning (opens in a new tab)Cambridge University Press · Phrasal-verb uses of back up