Viajo en marzo.

In Spanish, the subject pronoun is often omitted because the verb ending already tells you who the subject is.

• viajo = I travel / I’m traveling / I will travel (depending on context)
• The -o ending shows it is yo

So Viajo en marzo is completely natural. You could say Yo viajo en marzo if you want extra emphasis, contrast, or clarity, but it is not usually necessary.

Viajo comes from the infinitive viajar, which means to travel.

This is a regular -ar verb in the present tense:

• yo viajo = I travel
• tú viajas = you travel
• él/ella viaja = he/she travels
• nosotros viajamos = we travel
• ustedes viajan = you all travel
• ellos viajan = they travel

So in the sentence, viajo is the yo form.

Viajo is in the present tense.

However, in Spanish, the present tense is often used to talk about the future when the time is clearly stated. Since the sentence includes en marzo, it can naturally mean a future trip.

So Viajo en marzo can be understood as:

• I travel in March
• I’m traveling in March
• I’m going to travel in March
• I’ll travel in March

The exact English translation depends on context, but the Spanish sentence itself is very normal.

Spanish usually uses en with months to mean in.

• en marzo = in March
• en abril = in April
• en diciembre = in December

So Viajo en marzo literally matches I travel in March.

You would not normally say a marzo here.
A is used for other ideas, such as direction or certain time expressions, but not for in March.

Yes. This is very common in Spanish.

A present-tense verb can refer to the future when there is a time expression that makes the meaning clear:

• Viajo en marzo = I’m traveling in March
• Salgo mañana = I leave tomorrow
• Llegamos el lunes = We arrive on Monday

English does something similar in sentences like I’m leaving tomorrow.

In Spanish, months are normally written with lowercase letters, unlike in English.

So:

• marzo
• abril
• junio

not:

• Marzo
• Abril
• Junio

The same is true for days of the week:

• lunes
• martes
• domingo

They are only capitalized if they begin a sentence or are part of a title.

Yes, that is grammatically correct.

The difference is mostly about emphasis:

• Viajo en marzo = neutral, natural
• Yo viajo en marzo = emphasizes I

For example, you might use yo if you are contrasting yourself with someone else:

• Ella viaja en febrero, pero yo viajo en marzo.
  She travels in February, but I travel in March.

So both are correct, but the version without yo is more neutral.

Spanish verb endings usually show the subject.

For viajar in the present tense:

• viajo = I travel
• viajas = you travel
• viaja = he/she/you formal travels
• viajamos = we travel
• viajan = they/you all travel

The -o ending is the clue that the subject is yo.

You can simply use the same words and change the intonation in speech:

• ¿Viajo en marzo? = Am I traveling in March?

But in real conversation, if you are asking someone else, you would usually change the verb form:

• ¿Viajas en marzo? = Are you traveling in March?
• ¿Viaja usted en marzo? = Are you traveling in March? (formal)

Spanish does not usually need the helping verb do.

Put no before the verb:

• No viajo en marzo. = I’m not traveling in March.

This is the normal pattern in Spanish:

• Viajo = I travel
• No viajo = I do not travel / I’m not traveling

A learner may notice that the j is not pronounced like the English j in job.

A simple Latin American approximation is:

• viajo ≈ bee-AH-ho or vee-AH-ho

A few key points:

• v in Spanish is usually pronounced similarly to a soft English b/v sound
• j is like a strong h sound in most of Latin America
• the stress falls on via: via-jo

So the word is stressed as vi-A-jo.

Yes. That is also correct, and it explicitly sounds more future-oriented.

• Viajo en marzo = I travel / I’m traveling / I’ll travel in March
• Voy a viajar en marzo = I’m going to travel in March

Both are natural.
The second one is a little more explicit about the future, while the first is shorter and very common when the time expression already makes the future clear.