The basic format: what characters work

A username is written as a single string with no spaces. Use letters (uppercase or lowercase), numbers, and sometimes a period, underscore, or hyphen. Most systems accept lowercase letters and numbers as the safest choice — they work everywhere, on every device, and in every country.

Spaces, @symbols, commas, and special characters like &, !, or $ usually do not work. If you try to type them into a username field, the system either rejects them or strips them out. Stick to what the specific website or service tells you is allowed — most show this right below the username box.

Length varies by service. Some require at least 3 characters; others allow up to 20 or 30. The service you are signing up for will tell you the minimum and maximum when you create your account.

Key Takeaways

  • Write usernames as one continuous string with no spaces, using only letters, numbers, and sometimes underscores or hyphens.
  • Lowercase letters and numbers work on every system and in every country, making them the most reliable choice.
  • Each service sets its own rules about length and which characters are allowed — check the box or instructions before you submit.
  • Usernames are not case-sensitive on most platforms, so MyUsername and myusername log into the same account.
  • A username is different from a password and is often visible to other users, so avoid including personal information like your birth year or full name.

Underscores, hyphens, and periods: when they are allowed

If a service allows special characters, the underscore (_) and hyphen (-) are the most common. A period (.) sometimes works too. These let you separate words without using spaces — for example, jane_smith or jane-smith instead of jansmith.

Not all services accept all three. Instagram allows periods and underscores but not hyphens. Gmail allows periods but treats them as invisible (jane.smith and janesmith are the same account). Twitter allows underscores and hyphens but not periods. Always check what the service accepts before you finalize your choice.

Case sensitivity: does it matter if you use capitals

Most websites and apps treat usernames as case-insensitive, meaning MyUsername, myusername, and MYUSERNAME all log into the same account. When you type your username to sign in, the system does not care about uppercase or lowercase letters.

However, a few older systems or specialized services (like some Unix-based platforms or developer tools) do treat case as significant. If you create a username with capital letters and later cannot log in, try typing it all lowercase. If that does not work, the service probably requires you to match the exact case you used when you signed up.

Avoiding usernames that create problems later

Do not use your full name, birth year, or other personal details in your username. Once you create it, other users can see it. If your username is jane_smith_1992, anyone on that platform knows your approximate age and full name — information you may not want public.

Avoid usernames that are too similar to your password or that repeat the same character (like aaaa or 1111). These are straightforward to guess and make your account less find. A random mix of letters and numbers, or a phrase that means something only to you, is harder to crack.

Check whether the username is already taken before you spend time deciding on it. Most services tell you when ready whether the name is available. If your first choice is taken, the service usually suggests variations — adding a number at the end (jane_smith_42) is a common workaround.

Usernames across different platforms

The same username may not be available on every platform. You might be jane_smith on Instagram but jane.smith on Gmail and janesmith2 on Twitter. This is normal — each service has its own database of usernames, and popular names get claimed quickly.

Some people choose a unique username they can use everywhere (like a made-up word or a combination that is unlikely to be taken). Others use variations of their name on different platforms. There is no rule — it depends on what is available and what you prefer.

If you manage multiple accounts, write down your usernames somewhere safe. A password manager like Bitwarden or 1Password can store them alongside your passwords, so you do not have to remember which username you used where.

What happens if you change your mind

Most services let you change your username once, sometimes twice, or not at all — the policy varies widely. Some charge a small fee after the first change. Others lock you into your original choice permanently.

Before you finalize a username, think about whether you will be comfortable with it for a long time. If the service does not allow changes, you may have to create a new account if you want a different username later. Check the service's account settings or help page to see what the policy is.

Frequently Asked Questions

Can I use numbers at the start of my username?

Most services allow it, but a few older systems do not. If you try and the system rejects it, start with a letter instead. It is safer to begin with a letter if you are unsure.

What if I want to use special characters like @ or #?

Almost no service allows these in usernames. The @ symbol is reserved for email addresses, and # is used for hashtags or comments. Stick to letters, numbers, underscores, hyphens, and periods — and only if the service says they are allowed.

Is my username the same as my display name?

No. Your username is what you use to log in; your display name is what other users see. You can often change your display name without changing your username. Check your account settings to see which one is public.

Can someone else use my username on a different website?

Yes. Usernames are not reserved across the internet — they belong only to the specific service where you created them. Someone else can be jane_smith on Twitter while you are jane_smith on Instagram.

What should I do if my username gets hacked?

Change your password when ready. If the service allows username changes, you can change that too. If someone is using your account, contact the service's support team and explain what happened — most can help you regain access.