Ναι, ευχαρίστως.

A natural pronunciation is roughly:

• Ναι = neh
• ευχαρίστως = ef-ha-REE-stos

So the whole phrase sounds approximately like:

• neh, ef-ha-REE-stos

A few pronunciation notes:

• αι in Ναι sounds like e in yes or bed, not like English eye.
• ευ often sounds like ef before certain consonants, and here in ευχαρίστως it is pronounced ef.
• The stress falls on ρί: ευχα-ΡΙ-στως.

Ευχαρίστως means something like:

• gladly
• with pleasure
• I’d be happy to

So in Ναι, ευχαρίστως, it adds warmth and willingness. It is more than just yes. It means yes, gladly or yes, with pleasure.

It works in both formal and informal situations. It is polite and natural in many contexts.

For example, you could use it:

• with friends
• with a waiter
• with a colleague
• in a more formal interaction

It sounds a bit more courteous than a plain Ναι. So if someone offers you something or asks whether you would like to do something, Ναι, ευχαρίστως is a very good polite reply.

Use Ναι, ευχαρίστως when you want to sound more enthusiastic, warm, or polite.

Compare:

• Ναι. = Yes.
• Ναι, ευχαρίστως. = Yes, gladly / yes, with pleasure.

For example, if someone says:

• Θέλετε έναν καφέ; = Would you like a coffee?

You could answer:

• Ναι, ευχαρίστως.

That sounds more natural and friendly than a bare Ναι, especially when accepting an offer or invitation.

Yes. Very often ευχαρίστως alone is enough.

For example:

• Θα έρθετε μαζί μας; = Will you come with us?
• Ευχαρίστως. = Gladly.

Adding Ναι is possible, but not always necessary.
So both are natural:

• Ναι, ευχαρίστως.
• Ευχαρίστως.

The second one can sound slightly smoother and more idiomatic in some situations.

Yes, they are related in form, and learners often notice that.

• ευχαριστώ = thank you / I thank
• ευχαρίστως = gladly / with pleasure

Even though they look similar, they are used differently:

• ευχαριστώ is for thanking someone
• ευχαρίστως is for accepting something willingly

So do not confuse them. If someone offers you something, replying with ευχαριστώ usually means thank you, while ευχαρίστως means yes, gladly.

The comma separates the short response Ναι from the adverb ευχαρίστως.

It works a bit like English:

• Yes, gladly.
• Yes, with pleasure.

In writing, the comma helps show a slight pause. In speech, that pause may be very small, but the punctuation is normal and natural.

Ευχαρίστως is an adverb.

That means it describes the manner of accepting or doing something: gladly, willingly, with pleasure.

So in effect, Ναι, ευχαρίστως means:

• Yes — gladly
• Yes — with pleasure

This is why it fits especially well as a response to offers, invitations, and polite requests.

Yes. Depending on the situation, you might also hear:

• Βεβαίως. = Of course.
• Φυσικά. = Naturally / of course.
• Με χαρά. = With pleasure / gladly.
• Ναι, βεβαίως. = Yes, of course.

These are close in function, but ευχαρίστως has a particularly warm sense of gladly or I’d be happy to. That is why it is especially common when accepting an offer or invitation.