Bu kadar yorgunken evde kalmak daha mantıklı.

-ken means something like while, when, or in the state of being.

So yorgunken comes from yorgun (tired) + -ken, and it means:

• while tired
• when (someone is) tired
• being tired / in a tired state

In this sentence, Bu kadar yorgunken... means when you’re this tired or while this tired.

Turkish often uses -ken to set the situation for the main action:

• Evdeyken = while at home
• Küçükken = when (I/he/she) was little
• Yorgunken = when tired

Turkish often leaves out the subject when it is obvious from context.

In Bu kadar yorgunken evde kalmak daha mantıklı, the sentence is making a general statement, something like:

• When you’re this tired, staying home is more sensible
• or more generally, When one is this tired, staying home is more sensible

So sen is not necessary. Turkish commonly does this, especially in general advice or observations.

If you added sen, it would sound more explicitly directed at someone:

• Sen bu kadar yorgunken evde kalmak daha mantıklı.

But that version is less natural as written; Turkish would more naturally say:

• Senin bu kadar yorgunken evde kalman daha mantıklı.

That version clearly means it’s more sensible for you to stay home when you’re this tired.

Bu kadar means this much, this so, or more naturally in English, this in expressions like this tired.

So:

• bu kadar yorgun = this tired / so tired to this degree

It emphasizes the degree of tiredness.

Compare:

• çok yorgun = very tired
• bu kadar yorgun = this tired / so tired (to this extent)

A native English speaker might think bu kadar sounds unusual literally, but in Turkish it is a very normal way to say this much / this much of a degree.

Because kalmak means to stay/remain, and with locations it usually takes the locative case: -de / -da.

So:

• evde kalmak = to stay at home
• okulda kalmak = to stay at school
• otelde kalmak = to stay at a hotel

Using eve would mean to the house/home, which suggests direction toward home, not being/staying there.

Compare:

• eve gitmek = to go home
• evde kalmak = to stay home / stay at home

So evde is used because the action happens in that place, not toward that place.

Here kalmak functions like an English -ing form or infinitive used as a noun:

• evde kalmak = staying home / to stay home

In this sentence, that whole phrase acts as the subject:

• Evde kalmak daha mantıklı.
• Staying home is more sensible.

Turkish often uses the infinitive -mak / -mek this way to talk about actions in a general sense.

Examples:

• Beklemek zor. = Waiting is hard.
• Erken yatmak iyi. = Going to bed early is good.
• Evde kalmak daha mantıklı. = Staying home is more sensible.

Daha means more, so daha mantıklı means more sensible.

Turkish does not always need to state the second part of the comparison. English does this too:

• Staying home is better.
• Better than what? Maybe than going out, but it can be left unsaid.

So in Turkish:

• daha mantıklı = more sensible
• The comparison is implied by context, such as than going out, than pushing yourself, or than doing something else

If you want to state the comparison explicitly, Turkish can do that:

• Dışarı çıkmaktan daha mantıklı. = More sensible than going out.

But here, leaving it unstated sounds natural.

Yes, in a way there is a zero copula.

Turkish often makes present-tense sentences without an overt verb like to be when the predicate is a noun or adjective.

So:

• mantıklı = sensible
• daha mantıklı = more sensible

And the sentence simply means:

• Evde kalmak daha mantıklı.
• Staying home is more sensible.

You could add -dır in some contexts, but it is usually unnecessary and can sound more formal, emphatic, or textbook-like:

• Evde kalmak daha mantıklıdır.

That is grammatical, but the version without -dır is more natural in everyday speech.

Because -ken is a suffix-like ending attached directly to the word before it.

So:

• yorgun
  • -ken → yorgunken

This is normal in Turkish. A few similar examples:

• çocukken = when (I/he/she) was a child
• evdeyken = while at home
• öğrenciyken = when (I/he/she) was a student

The exact form can vary a little depending on what it attaches to, but it is written together with the word.

Yes, and that is actually a very useful comparison.

• evde kalmak daha mantıklı = staying home is more sensible
  This sounds more general.
• evde kalman daha mantıklı = it’s more sensible for you to stay home
  This sounds more directly tied to a specific person.

Why?

Because kalman is a verbal noun with a possessive ending:

• kalman = your staying / that you stay

So:

• Bu kadar yorgunken evde kalman daha mantıklı.
• When you’re this tired, it’s more sensible for you to stay home.

The original sentence with kalmak is still natural, but kalman can sound a bit more personal and targeted.

The word order is very natural:

• Bu kadar yorgunken = situation/background
• evde kalmak = the action being talked about
• daha mantıklı = the judgment about that action

So the structure is roughly:

[When this tired] + [staying home] + [is more sensible]

Turkish word order is flexible, but not all versions sound equally natural.

The given sentence is a very standard way to say it. You might also hear variations for emphasis, but the original order is probably the clearest and most neutral.

Basically yes, but historically it comes from the old form iken, which means while being / when being.

So you can think of it like this:

• yorgun + iken → yorgunken

In modern Turkish, learners usually just treat -ken as the usable ending.

This is why you may also see forms like:

• hasta iken → often hastayken
• evde iken → evdeyken
• yorgun iken → yorgunken

So for practical learning, it is best to remember:

• adjective/noun + -ken = while/when being ...

It is fairly neutral and natural.

It works in everyday speech and writing. It does not sound especially formal, and it does not sound slangy either.

If you wanted something more conversational, you might hear:

• Bu kadar yorgunsan evde kalmak daha mantıklı.
• If you’re this tired, staying home is more sensible.

That version uses -san (if you are) instead of -ken. Both are natural, but they feel slightly different:

• yorgunken = while/when tired
• yorgunsan = if you are tired

In this sentence, yorgunken sounds smooth and natural.