A meglepetésbuli márciusban lesz.

A is the Hungarian definite article, equivalent to English the.

So A meglepetésbuli means the surprise party.

A few useful things to know:

• Hungarian has no grammatical gender, so a does not mean the in a masculine/feminine/neuter sense. It is just the.
• The form a is used before consonant sounds.
• The form az is used before vowel sounds.

For example:

• a buli = the party
• az asztal = the table

Because it is a compound noun.

Hungarian very often joins nouns into a single word where English would often use two words. Here:

• meglepetés = surprise
• buli = party

Together, meglepetésbuli means surprise party.

This is very normal in Hungarian. Compound words are extremely common.

Márciusban means in March.

It is made from:

• március = March
• -ban = a case ending meaning in

So literally it is something like March-in.

Hungarian usually does not use a separate word for in here. Instead, it adds a suffix to the noun.

This is because of vowel harmony, which is a very important feature of Hungarian.

The suffix meaning in has two common forms:

• -ban
• -ben

Which one you use depends on the vowels in the word.

Since március has back vowels, it takes -ban:

• márciusban = in March

Compare:

• kertben = in the garden
• házban = in the house

So English speakers often think of this as one suffix with two harmonic versions.

Lesz is the future form of van / lenni, the verb to be.

In this sentence, lesz means will be:

• A meglepetésbuli márciusban lesz.
• The surprise party will be in March.

It is natural here because the sentence refers to a future event.

Yes, Hungarian often uses the present tense for future meaning when the time is clear from context.

However, in this sentence, lesz is very natural because it clearly points to a future occurrence: it will be in March.

A learner should remember:

• Hungarian can express future with present tense in many cases.
• But with to be, lesz is very common and natural for future meaning.

So A meglepetésbuli márciusban lesz sounds completely normal.

Because this is a normal and natural Hungarian word order.

A neutral version of the sentence is:

• A meglepetésbuli márciusban lesz.

This is roughly:

• The surprise party in March will-be.

Hungarian word order is more flexible than English word order, and it often depends on emphasis and information structure, not just grammar.

Putting lesz at the end here sounds neutral and natural.

Yes. That is also correct.

Both are grammatical, but the emphasis shifts a little.

• A meglepetésbuli márciusban lesz.
  Neutral statement about the party and when it will be.

• Márciusban lesz a meglepetésbuli.
  This puts more focus on March: It will be in March that the surprise party happens.

This kind of movement is very common in Hungarian.

Because Hungarian usually expresses meanings like in, on, at, and so on with suffixes attached to nouns, rather than with separate prepositions.

So:

• English: in March
• Hungarian: márciusban

This is one of the biggest structural differences between English and Hungarian.

English uses many prepositions.
Hungarian often uses case endings.

Normally, no.

In Hungarian, names of months are usually written with lowercase letters, so:

• március = March

This is different from English, where March is capitalized.

So márciusban is correctly written with a lowercase m.

Usually, in this sentence, you would keep a.

• A meglepetésbuli márciusban lesz. = The surprise party will be in March.

Without a, it sounds less natural in a normal context, unless you are speaking in a special style such as headlines, notes, or very clipped speech.

Since this refers to a specific party, the definite article is the expected choice.

A helpful approximation for English speakers is less.

A few details:

• sz in Hungarian is pronounced like English s
• so lesz sounds close to less
• this is different from Hungarian s, which sounds like English sh

This contrast is very important in Hungarian:

• sz = s
• s = sh

A simple learner-friendly guide:

• meglepetésbuli ≈ MEHG-leh-peh-TAYSH-boo-lee
• márciusban ≈ MAAR-tsee-oosh-bon

A few useful pronunciation points:

• Stress in Hungarian usually falls on the first syllable of the word.
• é is a long vowel, roughly like ay in say, but cleaner and tenser.
• cs sounds like English ch.
• s sounds like English sh.
• sz sounds like English s.

So pronunciation rules matter a lot in reading Hungarian.

Buli is a very common everyday word meaning party, but it is somewhat informal in tone.

That said, meglepetésbuli is a very normal and widely understood word for surprise party.

So the sentence sounds natural and everyday, not strange. It is just not especially formal or ceremonial.