Learn Hardcore Portuguese (Portugal): Hoje estou muito cansado, por isso vou deitar-me cedo. - Today I am very tired, so I am going to go to bed early.

ser – for permanent or defining characteristics (nationality, profession, personality, time, etc.)
estar – for temporary states or situations that can change (location right now, mood, physical state, weather right now, etc.)

Being tired is a temporary physical state, so you use estar:

Estou cansado. – I am tired (now / today).
Sou cansado. – sounds like “I am a tiring person” (a more permanent characteristic), and is much less common.

So Hoje estou muito cansado literally means “Today I am very tired (right now).”

Why does it end in cansado and not cansada?

Adjectives in Portuguese agree in gender and number with the noun or pronoun they refer to.

If the speaker is male: cansado
If the speaker is female: cansada

Examples:

A man: Hoje estou muito cansado.
A woman: Hoje estou muito cansada.
A group of men / mixed group: Estamos muito cansados.
A group of women: Estamos muito cansadas.

So the ending changes according to who is tired. In the given sentence, the speaker is assumed to be male (or grammatically masculine).

Why is there no eu (“I”) in Hoje estou muito cansado?

Portuguese usually drops the subject pronoun because the verb ending already shows who the subject is.

estou can only be I am (eu estou).
estás can only be you are (tu estás).
está is he/she/you(formal) is (ele/ela/você está), etc.

So Hoje estou muito cansado is completely natural and normal.
You can say Hoje eu estou muito cansado to emphasize I (contrasting with someone else or another day), but the default is to omit eu when it’s not needed for emphasis or clarity.

What does por isso literally mean, and how is it different from porque?

por isso literally means “for that (reason)” and functions like “so / therefore” in English. It introduces a result or consequence.

Hoje estou muito cansado, por isso vou deitar-me cedo.
= Today I am very tired, so I’m going to bed early.

porque means “because” and introduces the reason or cause.

Compare:

Vou deitar-me cedo porque estou muito cansado.
= I’m going to bed early because I’m very tired. (first the result, then the cause)
Estou muito cansado, por isso vou deitar-me cedo.
= I’m very tired, so I’m going to bed early. (first the cause, then the result)

So:

porque = because (introduces the cause)
por isso = so / therefore (introduces the consequence)

Can I replace por isso with então or logo?

Sometimes, but they’re not perfect synonyms:

então – often used like “so / then” in informal speech.
- Hoje estou muito cansado, então vou deitar-me cedo.
  Sounds natural in everyday conversation.
logo – in Portugal often means “soon / later on (today)” or “therefore” in more formal language.
In everyday speech, logo here would more likely be understood as “soon” rather than “therefore”, so:
- Hoje estou muito cansado, logo vou deitar-me cedo.
  Sounds formal/literary as “therefore”, or may be taken as “soon I’ll go to bed early”, depending on context and tone.

For a clear, natural “so / therefore” in European Portuguese, por isso is very safe and common.

Why is it vou deitar-me and not just vou deitar?

Because deitar-se is a reflexive verb when it means “to lie down / to go to bed”.

deitar on its own usually means “to lay something down / to throw away / to pour out (a liquid)”.
- Deitei o livro na mesa. – I put the book on the table.
- Deitei a água fora. – I threw the water away.

When you lie yourself down, Portuguese uses a reflexive pronoun:

deitar-se – to lie down, to go to bed.
Vou deitar-me. – I’m going to lie down / go to bed.
Vou deitar-te. – I’m going to lay you down (e.g. a child in bed).

So the -me is necessary here to show that the subject is acting on themself.

Why is there a hyphen in deitar-me, and can I also say vou-me deitar?

In European Portuguese, unstressed pronouns like me, te, se, nos, vos often attach to the verb with a hyphen. This is called enclisis (pronoun after the verb):

deitar + me → deitar-me
levantar + se → levantar-se
chamar + me → chamar-me

In vou deitar-me, the pronoun me is attached to the infinitive verb deitar, so we write it with a hyphen.

Yes, you can also say:

Vou-me deitar.

Here, the pronoun comes after vou (the conjugated verb), so it’s attached to vou as vou-me.

In European Portuguese:

Both Vou deitar-me and Vou-me deitar are used.
In formal writing, vou deitar-me (pronoun on the infinitive) is often preferred.
In everyday speech, vou-me deitar is also very common.

In Brazilian Portuguese, you’d normally hear Vou me deitar (pronoun before deitar, without hyphen), which is not the preferred pattern in Portugal.

Is vou here the future tense? Why not use a future form like deitarei-me?

Grammatically, vou is the present tense of ir (“to go”), followed by the infinitive deitar:

vou deitar-me = “I’m going to lie down / I’m going to bed.”

This ir + infinitive construction is a very common way to express near future / intention, very similar to English “going to + verb”.

Portuguese also has a synthetic future tense:

deitar-me-ei – I will go to bed (European norm)
deitarei-me – also seen, but less common in modern EP speech

However, in everyday spoken Portuguese, especially in Portugal:

vou deitar-me (or vou-me deitar) is far more natural than deitar-me-ei.
The synthetic future is used more in writing, formal speech, or set expressions.

So yes, it refers to the future, but structurally it’s a present of “ir” + infinitive, not the simple future ending.

Can hoje go in other places, like the end of the sentence?

Yes. Adverbs of time like hoje are quite flexible. These are all possible:

Hoje estou muito cansado, por isso vou deitar-me cedo.
(Common; emphasises “today” first.)
Estou muito cansado hoje, por isso vou deitar-me cedo.
(Also common; puts focus at the end of the first clause.)
Estou hoje muito cansado, por isso vou deitar-me cedo.
(Grammatically fine, slightly more marked / formal.)

Normally, you wouldn’t place hoje at the very end of the whole sentence here:

✗ Estou muito cansado, por isso vou deitar-me cedo hoje.
This is grammatically OK, but now hoje sounds more directly linked to vou deitar-me cedo (“I’ll go to bed early today”) rather than to being tired today. It’s a different emphasis, not wrong.

So position changes the nuance of what exactly is happening “today”.

Why is muito before cansado? Could I say cansado muito?

muito is an adverb of degree here (“very”). In Portuguese, adverbs that modify adjectives normally come before the adjective:

muito cansado – very tired
bastante cansado – quite tired
pouco cansado – not very tired

You cannot say ✗ cansado muito with the same meaning; that word order is not natural.

Compare with when muito modifies a verb:

Gosto muito de ler. – I like reading very much.
Trabalha muito. – He/she works a lot.

So:

muito + adjective → muito cansado
verb + muito → gosto muito, trabalho muito

What exactly does cedo mean here? How is it different from mais cedo?

cedo means early (relative to what is considered normal or expected).

Vou deitar-me cedo. – I’m going to bed early.

mais cedo means earlier (comparative):

Hoje vou deitar-me mais cedo. – Today I’ll go to bed earlier (than usual / than yesterday / than you).

So:

cedo – early (in general)
mais cedo – earlier (than some reference point, often implied)

How do I pronounce this sentence in European Portuguese?

Approximate European Portuguese pronunciation (very roughly using English-like hints):

Hoje – [ˈo.ʒɨ]
Like “OH-zh(uh)” (the final vowel is very reduced, almost like the “a” in “sofa”).
estou – [ɨʃˈto(w)]
Roughly “ush-TOH” (the es- often sounds like “ush” in Portugal).
muito – [ˈmũj.tu]
Nasal mũi- like “MOO-in” said through the nose: “MOO-een-tu”.
cansado – [kɐ̃ˈsa.ðu]
“kɐ̃-SA-du”, with the first vowel nasal and unstressed, final -do often sounds like -du.
por isso – [puˈɾi.su]
“pu-REE-su”, with a tapped r (like Spanish).
vou – [ˈvo(w)]
Like English “voh”.
deitar-me – [dɐjˈtaɾ-mɨ]
“day-TAR-m(uh)”; ei like “ay” in “day”, final -me is very reduced.
cedo – [ˈse.ðu]
“SE-du”, final -do again like -du.

Putting it all together quite naturally but slowly:

Hoje estou muito cansado, por isso vou deitar-me cedo.
≈ “OH-zh(uh) ush-TOH MOO-een-tu kɐ̃-SA-du, pu-REE-su VOH day-TAR-m(uh) SE-du.”