Du kan fråga mig när som helst.

Because after the modal verb kan (can / be able to), Swedish normally uses the bare infinitive — the infinitive without att.

So:

• Du kan fråga mig = You can ask me
• not Du kan att fråga mig

This is similar to English, where we say can ask, not can to ask.

Other Swedish modal verbs work the same way:

• Jag vill gå = I want to go
• Hon måste läsa = She must read
• Vi ska äta = We will / are going to eat

Because mig is the object form of jag.

In this sentence, du is the subject — the person doing the action — and mig is the object — the person receiving the action.

• jag = I
• mig = me

So:

• Du kan fråga mig = You can ask me

Compare:

• Jag frågar dig = I ask you
• Du frågar mig = You ask me

English has the same distinction: I/me, he/him, we/us, and so on.

När som helst is a fixed expression meaning any time, whenever, or at any time.

Word by word:

• när = when
• som helst adds the sense of any ... at all / whichever

So the phrase as a whole means something like whenever you want or at any time.

You will see the same pattern with other question words:

• vem som helst = anyone
• vad som helst = anything
• var som helst = anywhere
• hur som helst = anyway / however / in any way

So när som helst is a very common and useful expression.

Yes, it is completely natural and idiomatic.

It sounds like a normal, friendly way to tell someone:

• You can ask me any time
• Feel free to ask me whenever

Depending on tone and context, Swedish speakers might also say:

• Du får fråga mig när som helst — often feels a little more like you’re welcome to ask me any time
• Fråga mig när som helst — Ask me any time (more direct)

But your sentence is absolutely standard and natural.

Because in Swedish, time expressions and other adverbials often come near the end of the sentence, and that placement sounds very natural here.

The basic structure is:

• Du = subject
• kan fråga = verb phrase
• mig = object
• när som helst = time expression

So:

• Du kan fråga mig när som helst.

You can sometimes move adverbials for emphasis, but the usual neutral order is the one in your sentence.

For example:

• När som helst kan du fråga mig.

This is grammatically possible, but it sounds more marked or literary. The original sentence is the normal everyday version.

Mostly yes, but the exact feeling can depend on context.

In this sentence, kan does not just mean physical ability. It often means:

• you may
• you are allowed to
• you are welcome to
• feel free to

So Du kan fråga mig när som helst may sound a bit warmer than a strict literal you are able to ask me at any time.

Swedish kan is often broader than just ability, just like English can sometimes is.

Yes. Du får fråga mig när som helst is also natural, but it has a slightly different nuance.

• Du kan fråga mig när som helst = You can ask me any time
• Du får fråga mig när som helst = You may / you’re allowed to / please feel free to ask me any time

Får can sound a little more like giving permission, or warmly inviting someone to do it.

In many everyday situations, both are fine. If you want a neutral, standard version, kan works very well.

Fråga is pronounced roughly like FROH-ga, but with Swedish sounds.

A few helpful points:

• frå- has a long vowel sound, something like froh
• g is a hard g here
• the stress is on the first syllable: FRÅ-ga

The letter å is pronounced somewhat like the vowel in British more, though not exactly the same.

So a rough English-friendly guide is:

• fråga ≈ FROH-gah

Not always in everyday speech.

In careful pronunciation, mig is roughly may with a Swedish vowel quality, but in natural spoken Swedish it is very often pronounced more like mej.

That means learners often hear:

• mig sounding like mej

This is completely normal in speech.

The same thing happens with dig:

• dig is often pronounced dej

So when listening, do not be surprised if fråga mig sounds more like fråga mej.

Yes, du is the normal Swedish word for you, and modern Swedish uses it in almost all situations, including many that would be more formal in other languages.

So:

• Du kan fråga mig när som helst is normal and polite in most contexts.

There is also ni, but modern Swedish does not use it in exactly the same way that many languages use a formal you. In some situations ni can be polite, but it is much less central than formal you forms in languages like French or German.

For most learners, using du is the correct default.

Yes, very often. It is a very common phrase.

For example:

• Ring mig när som helst. = Call me any time.
• Du kan komma när som helst. = You can come any time.
• Hon kan börja när som helst. = She can start at any time.

So once you learn när som helst, you can reuse it in many everyday situations.