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Não sei quanto vou estudar hoje.

Não sei quanto vou estudar hoje.
I don’t know how much I am going to study today.

Breakdown of Não sei quanto vou estudar hoje.

hoje
today
ir
to go
estudar
to study
não
not
saber
to know
quanto
how much
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Questions & Answers about Não sei quanto vou estudar hoje.

What exactly does quanto mean in this sentence? Is it how much or how long?

In Não sei quanto vou estudar hoje, quanto most literally means how much:

  • Não sei quanto vou estudar hoje.
    → I don’t know how much I’m going to study today.

It’s about the amount of studying (effort, pages, chapters, time, etc.), but a native speaker will often understand it more vaguely as “how much study I’ll manage to do,” not necessarily a precise number.

If you specifically want to say how long (in time), you’d normally say:

  • Não sei quanto tempo vou estudar hoje.
    → I don’t know how long I’m going to study today.
Why is it quanto and not quantos or quanta here?

Because in this sentence quanto is not directly modifying a noun; it’s functioning more like an adverb (modifying the verb estudar):

  • quanto (vou estudar) → how much (I’m going to study)

When quanto directly modifies a noun, it agrees in gender and number:

  • quanto tempo – how much time (masc. sing.)
  • quanta água – how much water (fem. sing.)
  • quantos livros – how many books (masc. pl.)
  • quantas horas – how many hours (fem. pl.)

But in quanto vou estudar, there is no explicit noun after quanto, so it stays in its base form (masculine singular) and works adverbially: “how much (in quantity/extent).”

What is the difference between Não sei quanto vou estudar hoje and Não sei quanto tempo vou estudar hoje?

Both are possible, but they focus on slightly different things:

  • Não sei quanto vou estudar hoje.
    → vague amount of studying (effort, pages, productivity, or time – context-dependent).

  • Não sei quanto tempo vou estudar hoje.
    → specifically the length of time (e.g., 1 hour, 3 hours).

So:

  • If you mean time specifically, prefer quanto tempo.
  • If you just mean how much studying in general, quanto alone is fine and natural.
Could quanto here also mean “how many pages/chapters/exercises”? Or is it only time?

Yes, quanto by itself can cover different notions of amount, depending on context:

  • It could mean how many pages, how many exercises, how much material, or how long you’ll study.
  • The sentence leaves it intentionally vague, which is very natural in Portuguese.

If you want to be precise, you’d specify the noun:

  • Não sei quantas páginas vou estudar hoje. – I don’t know how many pages…
  • Não sei quantos exercícios vou fazer hoje. – I don’t know how many exercises…
  • Não sei quanto tempo vou estudar hoje. – I don’t know how long (in time)…
Why is there no eu before vou estudar? Would Não sei quanto eu vou estudar hoje be wrong?

In European Portuguese, the subject pronoun (like eu) is often dropped because the verb form already indicates the subject.

  • vou clearly shows 1st person singular (I go / I am going).

So:

  • Não sei quanto vou estudar hoje. – most natural, everyday version.
  • Não sei quanto eu vou estudar hoje. – grammatically correct, but sounds more emphatic or marked: “I don’t know how much I am going to study today (as opposed to someone else).”

In normal neutral speech in Portugal, you omit eu here.

What tense is vou estudar, and how does it compare to estudarei?

vou estudar is a periphrastic future: ir (present) + infinitive, very similar to English “I’m going to study”.

  • vou estudar → I’m going to study / I will study

estudarei is the synthetic future tense (simple future):

  • estudarei → I will study

In European Portuguese:

  • In spoken language, people very often use ir + infinitive (vou estudar).
  • The simple future (estudarei) is correct but tends to sound more formal, written, or sometimes a bit stiff in everyday conversation.

So:

  • Não sei quanto vou estudar hoje. – very natural in speech.
  • Não sei quanto estudarei hoje. – correct, but sounds more formal/bookish in modern European Portuguese.
Is Não sei quanto estudarei hoje acceptable, or does it sound strange in Portugal?

It is grammatically correct, but in everyday spoken European Portuguese it will usually sound:

  • Formal,
  • Written, or
  • Slightly old-fashioned in casual contexts.

In conversation, a Portuguese speaker would almost always say:

  • Não sei quanto vou estudar hoje.

Use estudarei mostly in formal writing, literature, or when you deliberately want a more elevated tone.

Can vou estudar also mean “I’m going (somewhere) to study,” like physically going?

Yes, ir has two roles:

  1. Main verb (to go physically)

    • Vou estudar na biblioteca.
      → I’m going (I will go) to study in the library.
      Here, vou = I go / I am going (movement), and estudar explains the purpose.

  2. Auxiliary for future (“going to” future)

    • Vou estudar hoje à noite.
      → I’m going to study tonight. (no physical movement implied)

In Não sei quanto vou estudar hoje, vou is understood as part of the future construction (auxiliary), not as physical movement. There is no location or movement context, so it’s naturally read as “I’m going to study (at some point today).”

Could I put hoje somewhere else in the sentence, like at the beginning? Does the meaning change?

Yes, you can move hoje; it stays the same basic meaning, but the focus can shift slightly.

All of these are grammatically correct:

  1. Não sei quanto vou estudar hoje.
  2. Hoje não sei quanto vou estudar.
  3. Não sei hoje quanto vou estudar. (less common, feels more marked)

Nuances:

  • 1 (original) is the most neutral, standard order.
  • 2 puts a little extra emphasis on hoje:
    → “Today, I don’t know how much I’m going to study.”
  • 3 is grammatically fine but less natural in casual speech; you’d usually pick 1 or 2.

In general, adverbs of time like hoje are flexible in position in Portuguese.

Why is não placed before sei? Can it ever go in another position?

In simple clauses, não normally comes directly before the main verb:

  • Não sei. – I don’t know.
  • Não quero. – I don’t want.
  • Não posso estudar. – I can’t study.

So:

  • Não sei quanto vou estudar hoje.
    → não
    • sei (main verb) is the standard pattern.

You cannot move não to the end or far away from the verb in neutral sentences. For example, you cannot say:

  • ✗ Sei não quanto vou estudar hoje. (wrong in standard Portuguese)
  • ✗ Sei quanto vou estudar hoje não. (wrong)

There are some more complex structures where não can appear with other elements (with pronouns, or in elliptical answers), but the basic rule is: não goes directly before the conjugated verb.

How would I say “I don’t know what I’m going to study today” instead of “how much”?

You change quanto (how much) to o que (what):

  • Não sei o que vou estudar hoje.
    → I don’t know what I’m going to study today.

Compare:

  • Não sei quanto vou estudar hoje. – I don’t know how much I’m going to study.
  • Não sei o que vou estudar hoje. – I don’t know what I’m going to study.

Both use the same vou estudar hoje structure; only the interrogative word changes.

Could I say Não sei quanto é que vou estudar hoje? What does é que do?

Yes, in European Portuguese you can say:

  • Não sei quanto é que vou estudar hoje.

é que is a very common emphatic structure in European Portuguese. Here it:

  • Adds a bit of focus/emphasis to the interrogative quanto,
  • Sounds more colloquial / conversational.

Meaning-wise, it’s basically the same as:

  • Não sei quanto vou estudar hoje.

The version without é que is slightly more neutral and is perfectly natural; the é que version just feels more like relaxed spoken Portuguese.

Would Brazilians say the sentence the same way, or is there a difference?

The sentence is perfectly understandable in Brazil:

  • Não sei quanto vou estudar hoje.

Some notes:

  • Brazilians might be more likely than Europeans to say Não sei o quanto vou estudar hoje, adding o before quanto; in Portugal this is less common and can sound more Brazilian.
  • Pronunciation and intonation will differ (European vs Brazilian accent), but grammar and basic structure are shared.

So your sentence is good standard Portuguese and works for both Portugal and Brazil, with just small stylistic preferences.