The difference is straightforward: "log in" is a verb phrase, "login" is a noun

Use log in (two words) when you are describing the action of entering your username and password. Use login (one word) when you are referring to the thing itself — the username, the password, the screen where you enter them, or the process as a noun.

The easiest way to remember: if you can replace the word with "sign in," you need two words. "I need to log in to my email" works the same way as "I need to sign in to my email." But "I forgot my login information" cannot become "I forgot my sign in information" — that does not sound right, which tells you the noun form is correct.

Most people mix these up because they sound identical when spoken aloud, and because tech companies themselves are inconsistent. You will see "Login" as a button label on websites even though the grammatically correct label would be "Log In." This inconsistency has made the one-word version so common that many dictionaries now list both as acceptable, though "log in" remains the technically correct verb form.

Key Takeaways

  • "Log in" (two words) is the verb phrase you use when describing the action: "I need to log in to check my bank account."
  • "Login" (one word) is the noun form you use for the thing itself: "My login is not working" or "Enter your login credentials."
  • If you can replace it with "sign in," use two words; if not, use one word.
  • Websites and apps often label buttons "Login" even though "Log In" is grammatically correct, which is why the distinction feels blurry.
  • Both forms are now widely accepted in informal writing, but two words remains the standard in formal or professional contexts.

When to use "log in" as a verb

Any time you are describing the action of entering credentials, use two words. "I logged in this morning," "You need to log in first," "She is logging in now" — all correct. The verb form describes what you are doing at that moment.

This is the most common use in everyday sentences. When someone asks "Did you log in yet?" they are asking whether you performed the action. When you tell someone "I cannot log in," you are saying the action is not working. These are all verb phrases, so they take two words.

When to use "login" as a noun

Use one word when you are talking about the login as an object or concept, not as an action. "My login is not working" refers to your username and password combination as a thing. "The login screen appeared" refers to the screen itself. "I need to reset my login information" refers to the credentials you use.

You will also see "login" used as an adjective in phrases like "login credentials," "login page," or "login attempt." In these cases, "login" is modifying the noun that follows it, which is why it stays one word. The same rule applies: you are not describing an action, so you do not use the two-word verb form.

Why tech companies ignore this rule

Most websites and apps label their button "Login" instead of "Log In," even though the button is asking you to perform an action. This is partly because one word takes up less space on a button, and partly because the distinction between the noun and verb forms has become so blurred in tech writing that many companies treat them as interchangeable.

You will also see "login" used as a noun in error messages like "Login failed" when the technically correct phrasing would be "Log in failed" or "Your login attempt failed." These inconsistencies have made the one-word version feel more natural to many people, especially those who spend a lot of time on computers. But the two-word form remains correct when you are describing the action itself.

How this rule applies to similar tech terms

The same pattern shows up with other tech verbs. "Sign in" and "signin" follow the same rule: use two words for the action, one word for the noun. "I need to sign in" versus "My signin failed." You will see "signin" used incorrectly on websites for the same reasons "login" is — space constraints and blurred distinctions.

"Log out" and "logout" work the same way. "I logged out" is correct; "The logout button" is correct. "Log on" and "logon" follow the pattern as well, though "log in" and "log out" are more common in modern usage.

What matters in practice

In formal writing — emails to your boss, documentation, support tickets — use "log in" as a verb and "login" as a noun. In casual messages, texts, or comments, either form is understood and accepted. Most readers will not notice the difference, and many will not care.

The real value in knowing the distinction is that it helps you write more clearly. When you use the correct form, your meaning is when ready obvious. "I cannot log in" is unambiguous — you are having trouble with the action. "My login is not working" is also clear — the credentials or system is the problem. Mixing them up does not usually cause confusion, but using them correctly makes your writing sharper.

Frequently Asked Questions

Is it wrong to use "login" as a verb?

Technically yes, but it is so common that many dictionaries now accept both forms. In formal writing, stick with "log in" as a verb. In casual communication, either form is understood. The distinction matters most when you want to write clearly and correctly.

Why do websites use "Login" on their buttons?

Partly because one word takes up less space, and partly because the distinction between noun and verb forms has become blurred in tech writing. Many companies treat "login" and "log in" as interchangeable, even though the two-word form is technically correct for the action.

Does this rule explore to "sign in" and "sign up"?

"Sign in" follows the same pattern as "log in" — two words for the action, one word for the noun. "Sign up" is slightly different because "signup" as a noun is more widely accepted and used, but the two-word form is still correct for the action: "I signed up yesterday."

What if I am writing for a company that uses "login" everywhere?

Follow your company's style guide. Consistency within a single organization matters more than following the grammatical rule. If your company has chosen to use "login" as both noun and verb, match that choice in your writing for that company.