Learn Hardcore Norwegian: I det siste har jeg vært trøtt.

The full phrase behind i det siste is something like i den siste tiden (“in the last time/period”).
When you drop tiden, what stays in fixed expression form is i det siste.

You cannot say:

✗ i den siste (wrong in this meaning)
✗ i siste (ungrammatical)

So you just have to learn i det siste as a set expression meaning “lately / recently.”

What tense is har jeg vært, and how does it compare to English?

Har jeg vært is the present perfect in Norwegian:

har = have (present of “to have”)
vært = been (past participle of å være = “to be”)

So har jeg vært = “I have been”.

It works very similarly to English present perfect:

I det siste har jeg vært trøtt.
= Lately I’ve been tired.

Both describe a state that started in the past and continues up to now or is relevant now.

What is the difference between har vært and var in this kind of sentence?

Har vært = have been (present perfect)
Var = was (simple past)

Compare:

I det siste har jeg vært trøtt.
= Lately I’ve been tired (and probably still am).
I går var jeg trøtt.
= Yesterday I was tired (a finished situation in the past).

You usually do not say:

✗ I det siste var jeg trøtt.

That sounds wrong/unnatural because i det siste points to a time period that includes the present, so you want har vært, not var.

Why is the word order I det siste har jeg vært trøtt and not I det siste jeg har vært trøtt?

Norwegian has the V2 rule (verb-second word order):

In a main clause, the finite verb (here: har) must be in second position, no matter what comes first.

In this sentence:

I det siste = first element (a time phrase)
har = verb in second position
jeg = subject
vært trøtt = rest of the predicate

So:

I det siste har jeg vært trøtt. ✅ (correct V2)

You cannot do:

✗ I det siste jeg har vært trøtt. (verb is not in second position → ungrammatical)

Can I also say Jeg har vært trøtt i det siste? Is there any difference?

Yes, Jeg har vært trøtt i det siste is fully correct and very natural.

Both:

I det siste har jeg vært trøtt.
Jeg har vært trøtt i det siste.

mean “Lately I’ve been tired.”

Differences:

I det siste har jeg vært trøtt slightly emphasizes the time frame (“Lately…”).
Jeg har vært trøtt i det siste starts with I, so the focus feels a bit more on “I have been…”, with the time frame added at the end.

In everyday speech, both are common. Use whichever feels more natural for the context.

What exactly does trøtt mean? Is it closer to “tired”, “sleepy”, or “exhausted”?

Trøtt most directly corresponds to “tired” or “sleepy”, depending on context.

After not sleeping much: Jeg er trøtt. = I’m tired/sleepy.
After a long day: Jeg er så trøtt. = I’m so tired.

Some useful contrasts:

trøtt – tired / sleepy, often linked to need for sleep.
sliten – worn out, exhausted, drained (physically or mentally).
søvnig – sleepy, drowsy (more “sleepy” than “tired”).

In I det siste har jeg vært trøtt, you would typically understand trøtt as “tired (a lot / often)”, possibly also “low on energy / sleepy.”

Is it correct to say Jeg er trøtt i det siste instead of Jeg har vært trøtt i det siste?

No, Jeg er trøtt i det siste is not natural Norwegian in this meaning.

For “lately / over a period of time up to now,” Norwegian wants the present perfect:

Jeg har vært trøtt i det siste. ✅
= Lately I’ve been tired.

Using er (simple present) with “i det siste” sounds wrong because i det siste refers to a stretch of time, not just your current state at this exact moment.

To talk only about right now, you would say:

Jeg er trøtt nå. = I’m tired now.

Is there an implied noun after siste in i det siste? What is being left out?

Yes. There is an implied noun referring to a time period, most often tiden (the time) or perioden (the period).

So you can think of:

i det siste ≈ i den siste tiden / perioden
(“in the last time/period”)

In everyday language, people almost always drop the noun and just say i det siste. The full version is possible but longer and sounds a bit more formal/emphatic:

I den siste tiden har jeg vært veldig trøtt.

Why is the preposition i used here? Could you use something else?

In time expressions, i is commonly used to mean “during / over / in” a period:

i helgen – over the weekend
i sommer – during the summer
i det siste – lately / in recent times

You wouldn’t normally replace i here with another preposition. Alternatives would change the phrase:

den siste tiden har jeg vært trøtt (no preposition; “the last while I’ve been tired”)
siden i fjor har jeg vært trøtt (“since last year I’ve been tired”)

So for this exact meaning, stick with i det siste.

Can I put i det siste in different positions in the sentence?

Yes, typical word orders include:

I det siste har jeg vært trøtt.
(time phrase in first position, then verb → V2 rule)
Jeg har vært trøtt i det siste.
(time phrase at the end)
Jeg har i det siste vært trøtt.
(time phrase inside the predicate; a bit more formal/bookish but correct)

All are acceptable. The most common in speech are usually:

I det siste har jeg vært trøtt.
Jeg har vært trøtt i det siste.

How do you pronounce trøtt, especially the ø and the double tt?

Approximate pronunciation (Bokmål, standard-ish):

trøtt: [trøt]

Key points:

ø: similar to the vowel in British English “bird” or the “u” in French “lune”, but with rounded lips. It’s a mid front rounded vowel.
Double tt: the t sound is short and crisp, and the vowel before it (ø) is also short. You do not say a long “øøø”.

Very rough English approximation: “trut”, but with the vowel of “bird” and a short, strong t at the end.

Is this sentence formal or informal? Is it okay to use in everyday conversation?

I det siste har jeg vært trøtt. is neutral in style:

Completely fine in everyday conversation.
Also fine in writing, messages, or slightly more formal contexts.

For very casual speech, people might add particles or intensifiers:

I det siste har jeg vært så trøtt, ass. (colloquial)
Jeg har vært skikkelig trøtt i det siste. (“really tired lately”)

But the base sentence you gave is standard and natural in almost any context.