Renten endrer seg i oktober.

Renten is the definite form of rente, so it means the interest rate rather than just interest rate in a general sense.

• en rente = an interest rate
• renten = the interest rate

Norwegian often uses the definite form where English also uses the.

Endrer seg means changes or changes itself.

The word seg is a reflexive pronoun, similar to itself / oneself in English. In Norwegian, the verb å endre seg is commonly used when something changes.

Compare:

• å endre noe = to change something
  
  • Jeg endrer planen. = I change the plan.
• å endre seg = to change
  
  • Planen endrer seg. = The plan changes.

So in this sentence, renten endrer seg means the interest rate changes.

Yes, but the meaning changes.

• å endre noe = to change something actively
• å endre seg = to change, to undergo change

So:

• Banken endrer renten. = The bank changes the interest rate.
• Renten endrer seg. = The interest rate changes.

In your sentence, the interest rate is the thing undergoing the change, so seg is natural.

Norwegian often uses the present tense to talk about the future, especially when the time is clear from context.

So Renten endrer seg i oktober can mean:

• The interest rate changes in October
• The interest rate will change in October

This works because i oktober clearly gives a time reference.

I oktober means in October.

The preposition i is used with months, seasons, and many time expressions:

• i januar = in January
• i sommer = in summer
• i morgen = tomorrow

So i oktober is the normal way to say in October.

This is the normal Norwegian main clause word order:

subject + verb + other elements

So here:

• Renten = subject
• endrer = verb
• seg = reflexive pronoun
• i oktober = time expression

A very common pattern in Norwegian is that the verb comes early, usually in the second position in main clauses.

Yes. That is also correct.

When a time expression comes first in a Norwegian main clause, the finite verb still stays in second position:

• Renten endrer seg i oktober.
• I oktober endrer renten seg.

This is an important Norwegian rule often called V2 word order.

Notice that after I oktober, you do not say I oktober renten endrer seg. The verb must come right after the first element.

In a normal main clause, reflexive pronouns like seg usually come after the finite verb:

• Han vasker seg. = He washes himself.
• Renten endrer seg. = The interest rate changes.

So endrer seg is the normal order here.

Usually, yes, in many everyday and financial contexts renten means the interest rate.

But rente can also mean interest more generally, depending on context. For example, it can refer to the interest paid on money.

In this sentence, renten is most naturally understood as the interest rate.

A rough guide for English speakers:

• endrer sounds approximately like EN-drer
• seg sounds roughly like sigh in many dialects, though pronunciation can vary

A few helpful notes:

• The r in Norwegian is usually pronounced more clearly than in many types of English.
• The g in seg is often not pronounced as a hard g like in go.
• Pronunciation varies by dialect, so you may hear some differences.

It can refer to both people and things.

So seg does not just mean himself/herself. It can also mean itself when the subject is a thing or idea.

Examples:

• Hun setter seg ned. = She sits down.
• Døren åpner seg. = The door opens.
• Renten endrer seg. = The interest rate changes.

By itself, it usually suggests that the interest rate changes at that time or will change then. It does not strongly tell you whether the change is one-time or part of a repeated pattern.

If you wanted to make repetition clearer, Norwegian would usually add more information, for example:

• Renten endrer seg ofte i oktober. = The interest rate often changes in October.
• Renten pleier å endre seg i oktober. = The interest rate tends to change in October.

So the original sentence most naturally sounds like a specific change associated with October.

The dictionary form is å endre = to change.

Endrer is the present tense form:

• å endre = to change
• endrer = change / changes

And in this sentence the full expression is å endre seg = to change.

A word-for-word breakdown is possible:

• Renten = the interest rate
• endrer = changes
• seg = itself
• i oktober = in October

So literally: The interest rate changes itself in October.

But that sounds unnatural in English. Natural English would simply be:

• The interest rate changes in October or
• The interest rate will change in October

This is a good example of how Norwegian uses a reflexive form where English usually does not.