Is it on accident or by accident?

The original and correct phrase is “by accident.” However, “on accident” is an error likely formed by people trying to say the opposite of “on purpose.” Although it’s a common mistake, the right way to say this phrase is “by accident.”

You can avoid this error by replacing “by accident” with “accidentally” (e.g., “I broke the lamp by accident” vs. “I broke the lamp accidentally”). Make sure not to replace it with “accidently,” as this is considered a common misspelling.