Eu vou guardar a metade do bolo para amanhã.

Vou guardar is the very common ir + infinitive future, similar to going to in English.

• Eu vou guardar = I’m going to save/keep
• Eu guardarei = I will save/keep

In Brazilian Portuguese, vou guardar is usually more natural in everyday speech. The simple future (guardarei) is correct, but it can sound more formal, literary, or less conversational.

So for normal spoken Brazilian Portuguese, Eu vou guardar a metade do bolo para amanhã sounds very natural.

You can absolutely omit Eu.

Portuguese often drops subject pronouns when the verb already makes the subject clear:

• Eu vou guardar...
• Vou guardar...

Both mean the same thing here.

In Brazilian Portuguese, speakers often include eu for emphasis, clarity, or rhythm, but it is not required in this sentence.

Both are possible, but a metade is very natural here because Portuguese often uses the definite article where English might not.

• a metade do bolo = half of the cake
• metade do bolo = also possible, slightly less explicitly framed as the half

In many cases, a metade de/do/da... sounds especially complete and standard when referring to a specific half of something.

So guardar a metade do bolo is a very normal way to say save half of the cake.

Do is a contraction of:

• de + o = do

The noun metade usually connects to what it is half of with de:

• a metade de o bolo → a metade do bolo

Since bolo is masculine singular, it takes o:

• o bolo
• de + o bolo → do bolo

Other examples:

• a metade da pizza = half of the pizza
• a metade dos livros = half of the books
• a metade das pessoas = half of the people

This is a very common learner question because English uses half in several ways.

In Portuguese, metade do bolo is the most natural way to mean half of the cake.

• a metade do bolo = half of the cake
• meio bolo is not the usual way to express that idea in this context

Meio/meia can mean half, but it behaves differently depending on the structure:

• meio quilo = half a kilo
• meia hora = half an hour
• metade do bolo = half of the cake

When talking about half of a specific object or whole, metade de/do/da... is often the safest and most natural choice.

Guardar can mean several related things, depending on context:

• to keep
• to save
• to put away
• to store

In this sentence, guardar suggests something like:

• save
• keep for later

So Eu vou guardar a metade do bolo para amanhã means the speaker is not going to eat all the cake now; they are keeping part of it for tomorrow.

It is more natural here than a verb like salvar, because salvar usually means to save/rescue or to save a file.

Here, para amanhã means for tomorrow.

The idea is:

• I’m saving half the cake so it can be eaten tomorrow

It does not mainly focus on duration, as until tomorrow would in English.

If you want a very literal idea:

• guardar para amanhã = keep/save something for use tomorrow

So the phrase is about purpose or intended time, not just how long the cake stays there.

Yes. In Brazilian Portuguese, pra is a very common informal contraction of para.

So these are both natural:

• Eu vou guardar a metade do bolo para amanhã.
• Eu vou guardar a metade do bolo pra amanhã.

Difference:

• para = more neutral / standard writing
• pra = very common in speech and informal writing

Both are widely used in Brazil.

Because para expresses purpose, destination, or intended time/use, which fits this sentence.

• guardar para amanhã = save for tomorrow

Por usually expresses things like:

• cause
• duration
• exchange
• movement through/by
• passive agent

So por amanhã would not sound right here.

A useful shortcut:

• para amanhã = for tomorrow
• por duas horas = for two hours

The given word order is very natural, but Portuguese allows some flexibility.

Standard order:

• Eu vou guardar a metade do bolo para amanhã.

Also possible:

• Vou guardar a metade do bolo para amanhã.
• Para amanhã, eu vou guardar a metade do bolo.

The most neutral version is the original one. Moving para amanhã to the front usually gives it extra emphasis.

Because metade is its own noun, and it is feminine:

• a metade

The gender of bolo does not change the gender of metade.

So:

• a metade do bolo
• a metade da pizza

In both cases, metade stays feminine because that is the gender of the noun metade itself.

A very natural spoken version would be:

• Vou guardar a metade do bolo pra amanhã.

Why?

• dropping eu is common
• pra is very common in speech

But the original sentence is already completely natural and correct:

• Eu vou guardar a metade do bolo para amanhã.

So the original is a good standard model, and the shorter version is a common everyday spoken variant.

In most Brazilian accents, do is pronounced roughly like doo, with a clear o sound, not like the English word do.

A rough pronunciation of the whole sentence might be:

• Eu vou guardar a metade do bolo para amanhã
• roughly: eh-o voh gwar-DAR a meh-TAH-jee do BOH-lo PAH-ra ah-ma-NYAH

A couple of useful notes:

• vou sounds roughly like voh
• guardar has stress on the last syllable: guar-DAR
• amanhã has stress on the last syllable and a nasal sound: a-ma-NHÃ

Exact pronunciation varies by region, but that is a reasonable Brazil-oriented guide.