It's my fault
Use this for past events, meaning "It was my fault."
A slightly more emphatic way to say it, literally "I have the fault/blame."
A more formal phrase for serious or professional situations, meaning "I take responsibility."
The glass broke. I'm sorry, it's my fault.
We arrived late because of the traffic, it's not your fault.
We lost the game because I didn't play well. It was my fault.
The client is angry. It's my fault, I forgot to send the report.
"Es mi culpa" is the standard and universally understood phrase across all of Latin America.
While "Es mi culpa" is perfectly fine, it's also very common to hear "Es culpa mía." This places the possessive adjective after the noun, a frequent pattern in Spain.
"Es mi culpa" is the most common expression. For past events, "Fue mi culpa" or "Yo tuve la culpa" are also frequently used.
"Es mi culpa" is standard. You might also hear "La culpa es mía," which emphasizes that the fault belongs to you and no one else.
"Es mi culpa" or "Fue culpa mía" are the standard ways. The intonation and accompanying gestures often carry as much meaning as the words themselves.
Saying "Es mi falta." — This is a common error. While "falta" can mean a mistake or foul, it doesn't mean "fault" in the sense of blame. "Falta" usually means a lack or absence of something (e.g., "hace falta sal" - it needs salt). The correct word for blame is "culpa."
Using the verb "estar": "Estoy mi culpa." — The fault is not a state you are in, so you can't use "estar." You use "ser" (es) because you are identifying what "it" is: "it is my fault." Correct: "Es mi culpa."
Confusing "por mi culpa" with "es mi culpa." — "Es mi culpa" is a complete sentence: "It is my fault." "Por mi culpa" means "because of my fault" and is used within a larger sentence. For example: "Llegamos tarde por mi culpa" (We arrived late because of my fault).