In English conversation, both "it's about time" and "finally" can be translated as "at last," but their nuances are quite different.

First, let's look at "it's about time." This expression is not simply "at last."

It can carry a hint of dissatisfaction or annoyance, like "Why did it take so long?" or "You should have done this earlier."

So in Korean, it's closer to "Now you're doing it," or "You should have done it earlier."

And an important point is that this expression usually comes with a past tense verb. It's characteristic to use the past tense while talking about the present situation.

It's about time you cleaned your room.
Now you're finally cleaning your room. You should have done it earlier.

It's about time we left.
Now it's time to go. It feels a bit late.

It's about time he got a job.
Now it's time for him to find a job.

It's about time you apologized.
Now you should apologize.

Looking at these, there's a common thread. It's not just about "waiting" but also carries the nuance of "Why are you only doing this now?"

So even among friends, saying it casually can feel a bit like pressure.

On the other hand, "finally" is a much more positive and neutral expression.

It simply means "at last" or "after waiting, it has happened."

The focus is on relief or joy rather than dissatisfaction. The emotion is much softer.

Finally, I passed the exam.
I finally passed the exam.

She finally arrived.
She finally arrived.

We finally finished the project.
We finally finished the project.

He finally called me back.
He finally called me back.

All these expressions follow the structure of "waiting → result → satisfaction." It's a feeling of achievement or resolution, not dissatisfaction.

Now, comparing the two expressions makes the differences clearer.

It's about time you called me.
Now you're finally calling me. Why did it take so long?

You finally called me.
You finally called me. I've been waiting.

Even though the situations are the same, completely different emotions are conveyed. The first sentence feels a bit sulky, while the second feels welcoming.

Let's compare one more example.

It's about time the bus came.
The bus is finally here. It's so late.

Finally, the bus came.
Finally, the bus has arrived. What a relief.

Here too, the first one conveys dissatisfaction, while the second conveys relief.

To summarize, it's good to remember this.

it's about time
waiting + dissatisfaction + feeling of being late

finally
waiting + resolution + satisfaction or relief

Lastly, here's a tip. If you want to keep the atmosphere light when someone has done something late, it's safer to use "finally."

Conversely, if you want to jokingly pressure a close friend or genuinely convey a feeling of "Why didn't you do this sooner?" you can use "it's about time."

"It's about time" can be a remark that puts pressure on someone depending on the situation, so be careful when speaking to a superior or elder.

If you want to congratulate or welcome someone without making them feel bad, the following expressions are safe to use.

When you're purely happy

"Finally!" At last!

When celebrating something you waited a long time for

"I'm so glad it happened." I'm really glad it finally happened.

When you've been waiting for someone to come

"I've been looking forward to seeing you." I've really missed you. (No hint of being late)

In formal situations

"We've been anticipating this." We have been looking forward to this moment.

Just mastering these differences will make expressing emotions in English conversation feel much more natural.