Learn Hardcore Japanese: raigetu siken ga arimasu.

In Japanese, time expressions (like “next month”) often appear without a particle. You could say 来月に試験があります, but the particle に is usually dropped in simple statements. Omitting it feels more natural and conversational.

Why is 試験 marked with が instead of は?

When you use existence verbs such as あります (to exist/happen), the thing that exists is marked by が. Here you’re simply stating “An exam exists (will take place).” If you switched to は, it would shift the focus or topic, implying contrast or known context (e.g. “As for the exam, …”), which doesn’t fit a neutral announcement.

What does あります mean in this sentence?

あります is the polite form of ある, which means “to exist” for inanimate things or events. In English it’s rendered as “there is/are” or “(an event) will take place.” So 来月試験があります means “There will be an exam next month.”

Can I use います instead of あります?

No. います is used for living creatures (people or animals). 試験 (exam) is not a living being, so you must use ある／あります for its existence.

Could I reorder the words as 試験があります来月?

No. Japanese word order is flexible, but time expressions generally come first. The usual pattern is:
• Time (来月) → Subject/Topic (試験が) → Verb (あります)
Putting 来月 at the end would sound unnatural.

How would I say “I have an exam next month” in Japanese?

You can personalize it with a pronoun and the verb ある:
私は来月試験があります。
Or more colloquially:
来月、試験があるよ。
Both mean “I have an exam next month.”

What nuance does this sentence carry?

It’s a neutral statement announcing the existence or happening of an exam. There’s no emphasis on who’s taking it or any contrast—just a simple fact. If you wanted to emphasize your own involvement, you’d add 私に (to me):
来月、私に試験があります。