Hoje estou mesmo cansado.

Because estar is normally used for a temporary state or condition, and being tired is seen as temporary.

• estou cansado = I am tired
• sou comes from ser, which is usually for more permanent characteristics

So Hoje estou mesmo cansado means that today, the speaker feels tired right now. Using sou cansado here would sound wrong for this meaning.

Here, mesmo is an intensifier. It adds emphasis and means something like:

• really
• truly
• definitely

So:

• Estou cansado = I’m tired
• Estou mesmo cansado = I’m really tired

This is a very natural use in European Portuguese.

No. Mesmo is a very flexible word in Portuguese.

It can mean different things depending on context, for example:

• the same
• even
• really / indeed
• exactly
• self / very

In Hoje estou mesmo cansado, it does not mean same. It means really or truly.

Portuguese often leaves out subject pronouns when they are already clear from the verb ending.

• estou already means I am
• so eu is not necessary

That is why Hoje estou mesmo cansado is completely natural.

You could say:

• Hoje eu estou mesmo cansado

but adding eu usually gives extra emphasis, contrast, or a more deliberate tone.

Because the adjective agrees with the person being described.

If the speaker is male, you use:

• cansado

If the speaker is female, you use:

• cansada

So:

• Hoje estou mesmo cansado = said by a man
• Hoje estou mesmo cansada = said by a woman

Agreement is very important in Portuguese adjectives.

Yes, absolutely. That is also correct and natural.

The difference is mainly one of nuance:

• muito cansado = very tired
• mesmo cansado = really tired

Muito focuses more on degree.
Mesmo often sounds a bit more emphatic or conversational, as if the speaker is insisting on how tired they feel.

Both are common.

Putting hoje first is a very natural way to set the time frame immediately.

• Hoje estou mesmo cansado = Today I’m really tired
• Estou mesmo cansado hoje = also possible

Both are grammatical, but starting with hoje makes today the first thing the listener notices. Portuguese often does this with time expressions.

Usually, for this meaning, mesmo goes before the adjective:

• Estou mesmo cansado

That is the most natural placement here.

Other placements may sound less neutral or change the emphasis. For a learner, the safest pattern is:

• estar + mesmo + adjective

So:

• estou mesmo cansado
• está mesmo difícil
• estamos mesmo atrasados

No. Cansado can refer to physical tiredness, mental tiredness, or even emotional exhaustion.

Depending on context, it can mean:

• sleepy or physically worn out
• mentally tired
• fed up or exhausted

So this sentence could mean the speaker is physically tired today, or just generally drained.

A rough English-friendly approximation is:

• OH-zh(uh) esh-TOH MEZH-moo kuhn-ZAH-doo

A few useful pronunciation notes:

• j in hoje sounds like the s in measure
• estou in European Portuguese often sounds more like esh-TOH than a fully clear es-TOU
• the final unstressed vowels are reduced, so hoje, mesmo, and cansado may sound less fully pronounced than an English speaker expects

A more accurate IPA-style version is roughly:

• [ˈoʒɨ ɨʃˈto ˈmeʒmu kɐ̃ˈzadu]

But for most learners, the main thing is to notice the reduced vowels and the soft zh sound.

Yes, very natural.

Hoje estou mesmo cansado sounds like normal everyday Portuguese from Portugal. It is simple, idiomatic, and something a native speaker could easily say in conversation.

It is a good model sentence because it shows several common features of Portuguese:

• omitted subject pronoun
• use of estar for a temporary state
• adjective agreement
• use of mesmo for emphasis