En mi cumpleaños, voy a soplar las velas de la tarta con mi familia.

In Spanish, en is often used for on or at with time expressions and events.

So:

• En mi cumpleaños = On my birthday
• En Navidad = At Christmas
• En verano = In summer

Using a here would not sound natural for this meaning. A is more commonly used for direction, indirect objects, or certain time expressions, but not for on my birthday in this sentence.

Voy a + infinitive is a very common way to talk about the near future in Spanish. It is like saying I’m going to blow out.

• voy = I go / I am going
• a = part of the future structure
• soplar = to blow

So:

• Voy a soplar las velas = I’m going to blow out the candles
• Soplo las velas would mean I blow out the candles or I am blowing out the candles, depending on context

Both can be grammatically correct, but voy a soplar sounds more natural when talking about a planned future action.

Because ir a + infinitive is a fixed structure in Spanish used to express the near future.

Examples:

• Voy a comer = I’m going to eat
• Vamos a salir = We’re going to go out
• Van a llegar = They’re going to arrive

So in your sentence:

• voy a soplar = I’m going to blow out

That a does not mean to in the usual movement sense here. It is just part of the future construction.

Yes, literally it means to blow the candles, but in context it means to blow out the candles.

Spanish often does not include a separate word for out in expressions like this when the meaning is already clear.

So:

• soplar las velas = to blow out the candles

This is the normal and natural way to say it.

Spanish uses definite articles (el, la, los, las) more often than English does.

Here, las velas means the candles, and it sounds natural because both speaker and listener know which candles are being talked about: the candles on the birthday cake.

Compare:

• Voy a soplar las velas = I’m going to blow out the candles
• Tengo velas = I have candles

In many everyday situations, Spanish prefers the article where English might leave it out or phrase things differently.

De la tarta means of the cake or more naturally on the cake / from the cake, depending on context.

Literally:

• las velas de la tarta = the candles of the cake

In natural English, we would usually say the candles on the cake, but Spanish commonly uses de to connect related nouns like this.

Other examples:

• la puerta de la casa = the door of the house
• el color del coche = the color of the car

So las velas de la tarta is the normal Spanish way to say the cake candles or the candles on the cake.

In Spain, tarta is a very common word for cake, especially a cake for a celebration like a birthday.

• tarta is very natural in Spain
• pastel exists too, but depending on the region, it can mean a different kind of cake, pastry, or dessert

Since this is Spanish from Spain, tarta is exactly what a learner should expect in a birthday sentence.

Yes, that is the most natural interpretation.

Con mi familia means with my family, so the idea is that this birthday event happens in the company of your family.

In practice, it usually means:

• your family is there with you
• you are celebrating with them

It does not necessarily mean that everyone is literally helping blow out the candles, although context could allow that. Most naturally, it just means I’m going to blow out the candles with my family there / while celebrating with my family.

Yes. Cumpleaños looks plural because it ends in -s, but as a noun it is treated as singular when it means birthday.

That is why you say:

• mi cumpleaños = my birthday
• tu cumpleaños = your birthday
• es mi cumpleaños = it’s my birthday

Even though the form looks plural, it functions as a singular noun in this meaning.

You could, but it sounds more wordy and less natural in most everyday situations.

• En mi cumpleaños = natural, simple, common
• En el día de mi cumpleaños = understandable, but more explicit and heavier

Most native speakers would normally choose En mi cumpleaños.

Not if you want the same meaning.

• En mi cumpleaños = on my birthday
• Para mi cumpleaños = for my birthday

So:

• En mi cumpleaños, voy a soplar las velas... = On my birthday, I’m going to blow out the candles...
• Para mi cumpleaños, voy a comprar una tarta = For my birthday, I’m going to buy a cake

They express different ideas.

It is not strictly necessary, but it is very normal and helpful.

En mi cumpleaños is an introductory time phrase, so the comma makes the sentence easier to read:

• En mi cumpleaños, voy a soplar las velas de la tarta con mi familia.

Without the comma, the sentence is still understandable:

• En mi cumpleaños voy a soplar las velas de la tarta con mi familia.

Both are acceptable.

You could say:

• En mi cumpleaños, soplaré las velas de la tarta con mi familia.

This means essentially the same thing: On my birthday, I will blow out the candles on the cake with my family.

The difference is mostly in tone:

• voy a + infinitive = very common, conversational, everyday future
• simple future (soplaré) = also correct, sometimes a bit more formal, planned, or written-sounding depending on context

In spoken Spanish, voy a soplar is often more common.

A rough pronunciation is:

• cum-ple-A-nyos

More carefully, in Spain-style pronunciation:

• cum-ple-A-ños

Notes:

• the ñ sounds like the ny in canyon
• the stress falls on a: cumpleAños

So it sounds approximately like koom-pleh-AH-nyos.

Yes, cumple is a very common informal short form of cumpleaños in Spain.

So:

• En mi cumple = On my birthday

It sounds casual and natural in conversation, especially with friends or family. But en mi cumpleaños is the full, standard form and is better for learners to know first.