Learn Hardcore Spanish (Spain): Estoy cansado, por eso me acuesto temprano. - I am tired, that's why I go to bed early.

Use estar for temporary states, feelings, and conditions. Estoy cansado means I’m tired right now. Ser describes inherent traits; soy cansado is not used for how you feel and would sound odd for a person. You can use ser with some activities or situations to say they are tiring (for example: Subir esa cuesta es cansado), and in Spain for a person you’d more naturally hear es cansino or es pesado.

Do I need to change cansado to cansada if I’m a woman?

Yes. The adjective agrees with the subject:

If you’re female: Estoy cansada.
Plural: Estamos cansados (mixed or all male) / Estamos cansadas (all female).

What does por eso do here, and could I use porque instead?

Por eso means therefore/so and connects two main clauses. Porque means because and introduces a subordinate clause. Both convey the cause–effect link, but the structure changes:

With porque: Me acuesto temprano porque estoy cansado.
With por eso: Estoy cansado, por eso me acuesto temprano.

Is the comma before por eso required?

It’s standard to separate por eso with a pause:

Comma: Estoy cansado, por eso me acuesto temprano (very common).
Semicolon: Estoy cansado; por eso me acuesto temprano (more formal).
Period: Estoy cansado. Por eso me acuesto temprano (also fine). You typically don’t add a second comma immediately after por eso unless you want a stronger parenthetical pause.

Why is me used with acuesto? Can I say acuesto temprano without it?

Acostarse is reflexive when you yourself go to bed, so you need the pronoun: me acuesto. Without the pronoun, acostar means to put someone else to bed: Acuesto al niño temprano. Saying acuesto temprano without an object is ungrammatical.

How do I conjugate acostarse in the present tense?

It’s stem-changing (o → ue) except in nosotros/vosotros:

yo: me acuesto
tú: te acuestas
él/ella/usted: se acuesta
nosotros/as: nos acostamos
vosotros/as: os acostáis
ellos/ellas/ustedes: se acuestan

What’s the difference between acostarse and dormirse?

Acostarse: to go to bed/lie down. It doesn’t imply sleep.
Dormirse: to fall asleep. It marks the moment you start sleeping. Example: Me acuesto temprano, pero me duermo tarde.

Does the present tense me acuesto express a habit or something I’m about to do?

Spanish present can do both. Me acuesto temprano can mean a habit (I usually go to bed early) or an immediate plan (I’m going to bed early tonight). Context or a time word like hoy or esta noche clarifies it.

Can I say me voy a acostar temprano or voy a acostarme temprano?

Both are correct and mean the same. With periphrastic future:

Pronoun before the conjugated verb: me voy a acostar temprano.
Pronoun attached to the infinitive: voy a acostarme temprano.

Is temprano an adjective or an adverb here? Does it change with gender?

Here it’s an adverb meaning early, so it doesn’t change: me acuesto temprano. As an adjective with a noun it does change: una hora temprana, los vuelos tempranos.

What’s the difference between temprano and pronto?

Temprano clearly means early.
Pronto often means soon, but in Spain it can also mean early in routine contexts, so me acuesto pronto is common. To avoid ambiguity (especially outside Spain), temprano is the safest choice for early.

Can I use así que, entonces, or por lo tanto instead of por eso?

Yes:

Así que: very common and informal in speech. Estoy cansado, así que me acuesto temprano.
Entonces: can work as so/then; slightly more sequential than causal. Estoy cansado; entonces me acuesto temprano.
Por lo tanto/por consiguiente: more formal. Avoid porque eso; the fixed connector is por eso.

Can I use the present progressive: Me estoy acostando temprano?

Only if you mean right now (I’m in the process of going to bed). For a plan (tonight) or a habit, use simple present (me acuesto temprano) or ir a + infinitive (me voy a acostar temprano).

Is estoy cansado the best way to say I’m sleepy?

Estoy cansado means I’m tired (physically/mentally). If you specifically mean sleepy, use tengo sueño. Both justify going to bed: Estoy cansado/tengo sueño, por eso me acuesto temprano.