Learn Hardcore Portuguese (Brazil): Quando está chovendo, eu fico em casa.

Está chovendo = it is raining (literally progressive, like English is raining).
- Very common in spoken Brazilian Portuguese.
- Focuses a bit more on the ongoing action or situation.
Chove = it rains / it’s raining (simple present).
- Also correct and natural.
- Sounds a little more neutral or sometimes more formal / written, especially in weather reports: Hoje chove em São Paulo.

In your sentence:

Quando está chovendo, eu fico em casa.
Quando chove, eu fico em casa.

Both can mean When(ever) it rains, I stay at home.
In everyday Brazilian speech, está chovendo is very common, so the original sentence sounds natural.

Can I omit the subject pronoun eu?

Yes.

Portuguese is a pro-drop language (it often drops subject pronouns because the verb ending already shows who the subject is).

So:

Quando está chovendo, eu fico em casa.
Quando está chovendo, fico em casa.

Both are correct.

Eu gives a bit more emphasis or clarity (especially in contrast: Eu fico em casa, mas eles saem.), but in a simple sentence like this, most Brazilians would be perfectly happy with Fico em casa.

Why do we use fico and not estou ficando?

Because this is a habitual action, and in Portuguese the simple present is the natural way to express habits and routines.

Fico em casa = I stay at home (as a general rule / habit).
Estou ficando em casa is grammatically possible, but:
- It sounds like a temporary trend: These days I’m staying at home (more than usual).
- Ficar
  - gerund can also suggest other meanings in different contexts (for example, ficar com alguém = to hook up/date someone), so it’s not the default here.

So for a rule or habit, use fico em casa, not estou ficando em casa.

What does ficar mean here, and how is it different from estar?

Ficar is a very flexible verb. Here, it mainly means to stay / remain.

Ficar em casa = to stay at home.
Estar em casa = to be at home (location/state).

Compare:

Eu estou em casa. = I am at home (right now; location).
Eu fico em casa quando está chovendo. = I stay at home when it’s raining (I don’t go out; this is my behavior).

Other common meanings of ficar (just for awareness):

ficar cansado = to become tired
ficar feliz = to become happy
ficar em São Paulo = to be located in São Paulo (for places: A loja fica no centro.)

In your sentence, it’s clearly to stay / remain.

Why is there a comma after chovendo?

Because the sentence starts with a dependent clause (time clause) introduced by quando:

Quando está chovendo, eu fico em casa.

In Portuguese:

When the subordinate clause (here: Quando está chovendo) comes first, you normally use a comma before the main clause (eu fico em casa).
If you reverse the order, the comma is usually optional:
- Eu fico em casa quando está chovendo. (normally written without a comma)

Can I say Quando chove, eu fico em casa? Is there any difference?

Yes, you can, and it’s very natural.

Quando chove, eu fico em casa.
Quando está chovendo, eu fico em casa.

Both can mean When(ever) it rains, I stay at home.

Nuance:

Quando chove feels a bit more general / timeless: whenever it rains.
Quando está chovendo focuses slightly more on the ongoing situation (when it is actually raining at that moment).

In practice, Brazilians use both a lot, and the difference is small.

Why is it em casa and not na casa?

Because em casa is a set expression that means at home.

em casa = at home (not necessarily emphasizing the physical building, but the idea of “home”).
na casa = in the / at the house (specific house, with the article a: em + a = na).

Compare:

Eu fico em casa quando está chovendo.
I stay at home when it’s raining. (my home, as a concept)
Eu fico na casa da minha avó.
I stay at my grandmother’s house. (a specific house)

Interestingly, with casa you often drop the article in fixed expressions:

em casa (at home)
para casa (to home)
de casa (from home), etc.

Can I change the word order to Eu fico em casa quando está chovendo?

Yes, absolutely.

Both are correct:

Quando está chovendo, eu fico em casa.
Eu fico em casa quando está chovendo.

The meaning is the same. The difference is just emphasis:

Starting with Quando está chovendo slightly emphasizes the condition / time.
Starting with Eu fico em casa slightly emphasizes what I do.

Is this sentence about right now, or about a general habit?

By default, with quando + present, it is understood as a general habit or rule:

Quando está chovendo, eu fico em casa.
= When(ever) it rains / whenever it’s raining, I stay at home.

Portuguese simple present is used very often for:

habits: Eu acordo às 7.
general truths: A água ferve a 100 graus.
repeated conditions: Quando está frio, eu uso casaco.

Context could also allow a more “right now” reading (e.g. talking about today’s plan), but the default is habitual.

Why do we use quando and not se?

Both quando and se can sometimes be translated as when or if, but they’re not interchangeable here.

quando = when / whenever, used for time:
- Quando está chovendo, eu fico em casa.
  When(ever) it’s raining, I stay home.
se = if, used for condition:
- Se chover, eu fico em casa.
  If it rains, I’ll stay home.

Difference:

Quando está chovendo, eu fico em casa.
Presents your staying at home as a regular pattern whenever that time/situation happens.
Se chover, eu fico em casa.
Emphasizes that rain is a condition for you to stay at home (more like a decision depending on the weather).

Both are fine sentences, but they express slightly different perspectives.

Could I say Quando estiver chovendo, vou ficar em casa? What changes?

Yes, this is also correct, but the focus is on the future.

Quando está chovendo, eu fico em casa.
General rule / habit (present tense used generically).
Quando estiver chovendo, vou ficar em casa.
Uses future subjunctive (estiver) + future / near-future (vou ficar).
This sounds like you are talking about a specific future situation or plan:
- Whenever it’s raining (in that future context), I will stay home.

So:

For a timeless habit: Quando está chovendo, eu fico em casa.
For a specific future plan: Quando estiver chovendo, vou ficar em casa.

Is está chovendo an example of the Portuguese continuous (progressive)? How is it formed?

Yes, está chovendo is the present continuous / progressive:

estar (conjugated) + gerúndio (the -ing form: -ando, -endo, -indo)

Examples:

estou estudando = I am studying
ela está trabalhando = she is working
nós estamos esperando = we are waiting
está chovendo = it is raining

In Brazilian Portuguese, this structure is very common, especially with physical actions and ongoing processes—quite similar to English be + -ing.

Are there more natural or colloquial ways Brazilians might say this?

Yes. Some common variants:

Quando tá chovendo, eu fico em casa.
(tá is colloquial for está, very common in speech.)
Quando chove, eu fico em casa.
Slightly more neutral / general, also common.
Dia de chuva eu fico em casa.
Literally: On rainy days I stay at home.

All of these sound natural in Brazilian Portuguese; choice depends on personal style and formality.

How do you pronounce Quando está chovendo, eu fico em casa in Brazilian Portuguese?

Approximate pronunciation (Brazilian, general):

Quando ≈ KWAN-doo (the an is nasal, like in French en)
está ≈ es-TAH (final a is open; es often sounds like “is”)
chovendo ≈ sho-VEN-doo (the ch is like English sh, en is nasal)
eu ≈ eh-oo but blended, almost like a single vowel glide
fico ≈ FEE-coo (clear ee sound, final o like “oo” in some Brazilian accents or like “o” in “so” in others)
em ≈ nasal ehn
casa ≈ KAH-za (soft z sound in the middle)

Spoken smoothly, it might sound like:

KWAN-doo es-TAH sho-VEN-doo, eh-oo FEE-coo ehn KAH-za.

Why does casa appear without an article here, while many nouns in Portuguese use articles?

Because casa is part of a fixed expression:

em casa = at home
para casa = to home
de casa = from home

In these expressions, no article is used:

Eu estou em casa. (I am at home.)
Eu vou para casa. (I am going home.)
Eu saí de casa cedo. (I left home early.)

If you talk about a specific house, you normally use the article:

na casa do João = in/at João’s house (em + a = na)
na casa azul = in the blue house

So in Quando está chovendo, eu fico em casa, it’s the idiomatic “home” use, so no article.