الموعد النهائي اليوم.

Because Arabic often leaves out the present-tense to be.

So الموعد النهائي اليوم is a complete sentence even without a verb. In grammar terms, it is a nominal sentence:

• الموعد النهائي = the topic/subject
• اليوم = the predicate, here a time expression

So the sentence naturally means The deadline is today.

If you were talking about the past or future, Arabic would normally use a verb, for example كان or, in Levantine, رح يكون.

Because النهائي is an adjective describing الموعد, and in Arabic adjectives must agree with the noun they describe in definiteness.

Here:

• الموعد = the date/appointment/deadline
• النهائي = the final

So together they mean the final date or the deadline.

If the noun were indefinite, the adjective would also be indefinite:

• موعد نهائي = a final date / a deadline

This is very different from English, where the adjective does not change.

Here, النهائي is an adjective, not part of an iḍāfa.

That means the structure is:

• noun + adjective
• الموعد النهائي = the final deadline/date

A good clue is that the adjective also has ال. In Arabic, adjectives often come after the noun.

A different structure would be something like:

• موعد النهاية = the time/date of the end

That would be an iḍāfa. So learners should not think every two-word noun phrase is an iḍāfa.

Because اليوم is simply the normal Arabic word for today.

Even though English says today without the, Arabic uses اليوم, literally based on the day, as a fixed time expression. So the ال here is completely normal.

This is one of those places where you should not translate the article too literally.
In real usage:

• اليوم = today
• not necessarily the day

Because it is functioning as the predicate: today is the information being said about the deadline.

So the sentence is structured like:

• الموعد النهائي = what we are talking about
• اليوم = what we are saying about it

This order is very natural.

You can also move اليوم to the front for emphasis:

• اليوم الموعد النهائي

That feels more like Today is the deadline with extra focus on today.

A careful, formal reading would be close to:

• al-mawʿid an-nihāʾī al-yawm

A more Levantine-style pronunciation might sound more like:

• el-mōʿed en-nihāʾi il-yōm

A few useful pronunciation notes:

• In النهائي, the ل of ال is absorbed into ن, because ن is a sun letter. So you hear en-nihāʾi, not el-nihāʾi.
• In اليوم, the ل is still pronounced, because ي is not a sun letter.
• موعد contains ع, which English speakers usually find difficult. It is better to pronounce it imperfectly than to drop it completely.

It is understandable, but it sounds fairly formal and closer to MSA or formal written Arabic than everyday casual Levantine.

In daily speech, a Levantine speaker might choose something more conversational depending on context, such as:

• آخر مهلة اليوم = the last deadline / final deadline is today
• آخر موعد اليوم
• something more specific like التسليم اليوم if the context is submitting something

So the given sentence is not wrong at all, but it has a more formal tone.

Yes, you can.

• الموعد النهائي اليوم
• الموعد النهائي هو اليوم

Both are possible.

Adding هو can make the sentence sound a bit more explicit or emphatic, like The deadline is today with extra stress on the structure. But in Arabic, especially in everyday speech, it is very common to leave it out.

So for a learner, the safest rule is:

• without هو = normal and very common
• with هو = also possible, often a little more emphatic or formal

A fully vocalized formal version would usually be:

• الموعدُ النهائيُّ اليومَ

Why?

• الموعدُ is the subject/topic, so it is nominative
• النهائيُّ matches it as an adjective
• اليومَ is a time expression, so it is often treated as an adverbial accusative

In Levantine, though, learners usually do not pronounce or worry about these case endings, so in practice you will mostly just see:

• الموعد النهائي اليوم