Login, Log in, or Log‑in: Which is Correct?

The button says "Login", the help text asks you to "log‑in", and the error message announces that your "log in" has failed. The system might be perfectly capable of recognising you. Its copy appears less certain about itself.

Start with the Action

"Please log in to your account" uses a phrasal verb: the verb "log" followed by "in". You can change its tense, or place another word between its parts: "She logged in", "I'm logging in", and "The system logged me in".

"Please login to your account" is common enough to be understood, but it doesn't follow that verb pattern. I'd change it to "Please log in to your account".

Cambridge's entry for the verb gives "log in" and "log on" as phrasal verbs.

Naming the Process, Page, or Details

A noun does a different job: "The last login failed", "Open the login page", or "Check the login history". Here, "login" names an event or modifies another noun. It isn't asking the reader to perform the action.

Cambridge also recognises "login" and "log‑in" as noun forms. The hyphenated noun isn't wrong; it just isn't the spelling I use.

I prefer "login" because it keeps interface copy compact and gives a clear contrast with the two‑word verb.

Be more careful with "your login". Depending on the context, it might mean a username, account credentials, a previous session, or the act of entering the system. A sentence can have the correct spelling and still leave the reader guessing. If you need a username, ask for the username. If you need an email address, say so.

Log in, Sign in, and Signing up

"Sign in" is another familiar label for the action. If that's what the rest of the service uses, I stick with it and use the matching "Sign out".

"Sign up" usually describes registration, whilst "Sign in" describes entering an existing account. Those phrases differ by only one small word. I prefer "Create an account" where that difference might be missed.

Neither "log in" nor "sign in" specifies an authentication method, and recognising an account does not decide what it may access. Those are separate technical questions; the interface label describes the visitor's task.

A function named login or a route ending in /login/ can keep its fixed spelling whilst the visible button uses the two‑word verb. Renaming a public route is an engineering change, with consequences beyond the sentence you are editing.

What Should the Button Say?

For the button, I use "Log in". It also works as an invitation above the form. A navigation item called "Login" can instead name the destination, so that spelling isn't automatically a mistake.

"Log in", "Log out", and "Create an account" tell the visitor what the controls do. "Your login" still leaves them to guess what we're asking for.

The button "Log in" and the message "Your last login was yesterday" follow the same grammatical rule. They shouldn't share one translation key just to make their spelling match.

A label suitable for a heading may not fit into a sentence. Translators may need different word order or forms for each context, too. Reusing a string saves very little if it prevents anyone from writing a natural sentence around it.