Извини, я опоздал.

Извини is the informal singular imperative of извинить, so it means something like forgive me or sorry when speaking to one person you address informally.

It is used:

• with friends
• family
• children
• people your age in casual situations

If you need to be polite or are speaking to more than one person, use Извините instead.

So:

• Извини, я опоздал. = informal
• Извините, я опоздал. = polite/formal or plural

In Russian, pronouns are often omitted when the verb already makes the subject clear. But in the past tense, Russian verbs do not show person clearly the way present-tense verbs do. They show:

• gender
• number

So опоздал means was late / arrived late for a masculine singular speaker, but it does not by itself explicitly mean I.

That is why я is very natural here:

• Я опоздал = I was late / I’m late / I arrived late

You can omit я if the context already makes it obvious:

• Извини, опоздал.

But for learners, я опоздал is the safest and clearest version.

In the Russian past tense, verbs agree with the subject in gender and number.

So:

• я опоздал = said by a man
• я опоздала = said by a woman
• мы опоздали = said by more than one person

This is one of the big differences from English: past-tense verbs in Russian can show whether the speaker is masculine or feminine.

Опоздал is the past tense of опоздать, which means to be late or to arrive late.

This is a perfective verb. In this sentence, it refers to a completed fact: the speaker ended up being late.

Compare:

• опоздать → perfective
• опаздывать → imperfective

Examples:

• Я опоздал. = I was late / I arrived late.
• Я опаздывал. = I was being late / I used to be late / I was running late, depending on context.

In everyday apologies, Я опоздал is very common.

It can mean either, depending on context.

Russian опоздать covers both ideas:

• being late
• arriving after the expected time

So Извини, я опоздал may be understood as:

• Sorry, I’m late
• Sorry, I was late
• Sorry, I arrived late

English chooses among these more explicitly, but Russian often leaves that to context.

There is a comma because the sentence has two parts:

• Извини = a standalone imperative
• я опоздал = a separate clause

So the comma works much like in English:

• Sorry, I’m late.

Russian punctuation often separates short spoken units like this very clearly.

Yes, it is completely natural.

A Russian speaker might also say:

• Извини, я опоздал.
• Прости, я опоздал.
• Извини, что я опоздал. = Sorry that I was late.
• Прости, что опоздал. = Sorry that I was late.

The version with что is a little more explicit, but your sentence is already very normal and idiomatic.

Both can mean sorry or forgive me, and both are common.

Very roughly:

• Извини often sounds like excuse me / sorry
• Прости can sound a bit more personal or heartfelt, like forgive me

But in many everyday situations, they overlap a lot.

For being late:

• Извини, я опоздал = very normal
• Прости, я опоздал = also normal, sometimes a bit warmer or more emotional

The stress is:

• извинИ
• я
• опоздАл

A rough pronunciation guide:

• Извини ≈ iz-vee-NEE
• я ≈ ya
• опоздал ≈ a-pa-zDAL

A few useful notes:

• Unstressed о in Russian is often pronounced more like a
• Final л in опоздал is clear and pronounced

So the whole sentence sounds roughly like:

• iz-vee-NEE, ya a-pa-zDAL

Not with Извини, unless you are on informal ты terms with that person.

For a teacher, boss, older person, or stranger, say:

• Извините, я опоздал. if the speaker is male
• Извините, я опоздала. if the speaker is female

So the important distinction is:

• Извини = informal singular
• Извините = formal/polite or plural

Not literally.

Literally, Извини is an imperative meaning something like forgive me or excuse me.

Russian often uses this kind of imperative where English uses sorry.

So even though the literal structure is different, the natural translation is often just:

• Sorry
• I’m sorry
• Excuse me

That is why Извини, я опоздал is idiomatic even though word-for-word it is closer to:

• Forgive me, I was late