Όταν κρυώνω, κουμπώνω καλά το σακάκι μου μέχρι πάνω.

Because the sentence describes a habitual or general action:

• Όταν κρυώνω = When(ever) I get cold / when I’m cold
• κουμπώνω καλά το σακάκι μου μέχρι πάνω = I button my jacket up well/all the way up

In Greek, the present tense is often used for things that happen regularly or whenever a situation occurs.

So this is not necessarily about one specific moment right now. It means something like:

• Whenever I feel cold, I button my jacket all the way up.

If you were talking about one specific past event, Greek would use different tense forms.

Όταν means when.

In this sentence, it introduces a time clause:

• Όταν κρυώνω = When I’m cold / When I get cold

A useful point for learners: όταν can often mean whenever in sentences about repeated actions, even if English just says when.

So here the sense is:

• Whenever I get cold, I button up my jacket.

Greek often uses the verb κρυώνω to express the idea I’m cold or I feel cold.

So:

• κρυώνω literally comes from the idea of becoming cold / feeling cold
• but in everyday English translation, it is often simply I’m cold

This is very natural Greek. A learner might expect a structure like I am cold, but Greek usually prefers the verb here.

Compare:

• Κρυώνω. = I’m cold.
• Ζεσταίνομαι. = I’m hot / I’m getting warm.

So this is one of those places where Greek and English use different grammar for the same idea.

Κουμπώνω means to button, to fasten, or more generally to do up clothing.

Here:

• κουμπώνω το σακάκι μου = I button my jacket / I do up my jacket

It comes from κουμπί, which means button.

Depending on context, English might translate it as:

• button
• button up
• do up
• fasten

In this sentence, button up is probably the most natural English equivalent.

Yes, καλά literally means well, but here it has a slightly more practical sense.

In this sentence:

• κουμπώνω καλά το σακάκι μου means something like
  • I button my jacket properly
  • I fasten my jacket securely
  • I button my jacket up well

So καλά does not just mean skillfully. It means the speaker closes the jacket properly/tightly/securely, especially because they feel cold.

Μέχρι πάνω literally means up to the top.

In this sentence, it means the speaker buttons the jacket:

• all the way up
• right up to the top
• up to the neck/collar area

So:

• κουμπώνω καλά το σακάκι μου μέχρι πάνω = I button my jacket all the way up

This is a very natural expression in Greek for clothing that can be buttoned or zipped high up.

Because Greek normally uses the definite article together with possessives.

So Greek says:

• το σακάκι μου = literally the jacket my
• natural English: my jacket

This is completely normal Greek structure.

Other examples:

• το σπίτι μου = my house
• ο αδερφός μου = my brother
• η τσάντα μου = my bag

For English speakers, the article may feel extra, but in Greek it usually belongs there.

It is in the accusative case, because it is the direct object of κουμπώνω.

The speaker is doing the action to the jacket:

• κουμπώνω what?
• το σακάκι μου

So:

• το = neuter singular accusative article
• σακάκι = neuter singular noun
• μου = possessive clitic meaning my

Because σακάκι is a neuter noun, the nominative and accusative forms look the same here, but its role in the sentence is direct object.

The comma separates the subordinate time clause from the main clause:

• Όταν κρυώνω, = When I’m cold,
• κουμπώνω καλά το σακάκι μου μέχρι πάνω. = I button my jacket all the way up.

This is very similar to English, where a comma is also commonly used when a when-clause comes first:

• When I’m cold, I button my jacket all the way up.

So the punctuation works in a familiar way here.

Yes. Greek word order is more flexible than English word order.

The sentence as given is very natural:

• Όταν κρυώνω, κουμπώνω καλά το σακάκι μου μέχρι πάνω.

But Greek could move some parts around for emphasis, for example:

• Όταν κρυώνω, το σακάκι μου το κουμπώνω καλά μέχρι πάνω.
• Κουμπώνω το σακάκι μου καλά μέχρι πάνω όταν κρυώνω.

Not every version sounds equally neutral, though. The original sentence is a very good everyday word order.

A useful basic pattern to remember is:

• time clause + main verb + object + extra detail

Usually σακάκι means jacket, especially a jacket-like outer garment or blazer.

Depending on context, it can mean:

• a casual jacket
• a suit jacket
• a blazer

In this sentence, because of κουμπώνω and μέχρι πάνω, the exact English word might vary depending on the garment, but jacket is a very reasonable translation.

If the speaker meant a heavy winter coat, Greek might also use words like:

• μπουφάν = jacket / coat
• παλτό = coat

But σακάκι itself is perfectly normal Greek.

A Greek speaker would hear it as a simple, natural statement about personal habit.

It sounds like:

• Whenever I feel cold, I button my jacket right up.

The tone is:

• neutral
• everyday
• conversational
• practical

Nothing in the sentence is especially formal or literary. It is the kind of sentence you could easily hear in ordinary speech.