Я допью чай и пойду спать.

Because допью is from a perfective verb: допить.

In Russian, perfective verbs do not have a true present tense. What looks like a present-tense form is actually used for the simple future:

• я допью = I will finish drinking
• not I am finishing drinking

So in this sentence:

• Я допью чай = I’ll finish my tea

This is one of the most important patterns in Russian:

• imperfective present = present meaning
• perfective “present” forms = future meaning

The prefix до- adds the idea of finishing something that is already in progress or doing something to the end.

So:

• пить = to drink
• выпить = to drink up / drink (a whole amount)
• допить = to finish drinking what was left

That means Я допью чай often suggests:

• the tea is already there,
• the speaker has already started it or intends to finish the remaining amount.

So допью is not just I will drink tea, but more specifically I’ll finish my tea.

Here чай is the direct object, so it is in the accusative case. For an inanimate masculine noun like чай, the accusative looks the same as the nominative:

• nominative: чай
• accusative: чай

So:

• допью чай = I’ll finish the tea / my tea

You may sometimes see the genitive after certain verbs or in partitive-style meanings, but in this sentence the normal expected form is чай.

Because the sentence talks about a future action, not something happening right now.

• иду = I am going / I go
• пойду = I will go / I’ll set off

Here пойду comes from the perfective verb пойти, which often means to start going or to set off.

So:

• пойду спать = I’ll go to sleep / I’ll go to bed

Using иду спать would usually mean something more immediate, like:

• I’m going to bed now
• I’m off to sleep now

But in Я допью чай и пойду спать, the speaker is talking about the next step in the future, so пойду is natural.

Because пойти/идти + infinitive is a very common Russian pattern meaning go somewhere in order to do something or simply go and do something.

So:

• пойти спать = to go to sleep / go to bed
• пойти есть = to go eat
• пойти работать = to go work

In English we often say go to bed or go to sleep, while Russian often uses go + infinitive directly.

So пойду спать is a very standard, idiomatic way to say:

• I’ll go to bed
• I’ll go to sleep

depending on context.

Because after verbs like идти / пойти, Russian often uses an infinitive to express the purpose or the action that follows.

In this sentence:

• пойду спать

literally means something like:

• I will go sleep

But natural English is:

• I’ll go to sleep
• I’ll go to bed

So the infinitive спать is not strange here; it is exactly the normal Russian structure after пойти in this kind of phrase.

Yes, there is a small but useful difference.

• пойду спать = I’ll go to bed / I’ll go to sleep
  • focuses on the decision or movement toward bed/sleep
• лягу спать = I’ll lie down to sleep
  • focuses more on physically lying down

In many everyday situations they can both translate as I’ll go to bed, but they are not identical.

Your sentence sounds very natural because:

• first action: finish tea
• next action: go to bed

That sequence fits пойду спать very well.

Because the sentence describes two completed, one-time future actions in sequence:

1. допью чай — I’ll finish the tea
2. пойду спать — then I’ll go to bed

Perfective is natural here because the speaker means:

• first one thing will be completed,
• then another single action will happen.

If you used imperfective verbs, the meaning would shift and might sound less like a simple planned sequence of completed steps.

So perfective here gives the feeling:

• I’ll finish my tea and then I’ll go to sleep.

Grammatically, и means and, but in this sentence it strongly suggests a sequence:

• Я допью чай и пойду спать.
• I’ll finish my tea and go to bed.

Because of the meaning of the verbs, English often naturally adds then:

• I’ll finish my tea, then go to bed.

Russian does not need a separate word like потом here, because the sequence is already clear from context and aspect.

Yes, very often.

Russian commonly drops personal pronouns when the verb ending already makes the subject clear.

So both are possible:

• Я допью чай и пойду спать.
• Допью чай и пойду спать.

Both mean the same thing: I’ll finish my tea and go to bed.

Including Я can:

• add emphasis,
• make the sentence clearer in context,
• or simply sound more explicit.

Not exactly. Допью чай is more specific than that.

It means I’ll finish the tea or I’ll finish my tea. It suggests completion, not just the act of drinking some tea.

If you wanted a more general idea like I’ll drink tea and then sleep, Russian might use a different verb or phrasing, depending on the context.

So the important nuance is:

• допью чай = finish drinking the tea
• not just drink tea

Russian has no articles like a, an, or the.

So чай can mean:

• tea
• the tea
• some tea
• my tea

The exact meaning depends on context.

In this sentence, because of допью, English will usually translate it as:

• I’ll finish my tea or
• I’ll finish the tea

The Russian noun itself does not show that difference with an article.

The most natural translations are:

• I’ll finish my tea and go to bed.
• I’ll finish my tea and go to sleep.

Both work well.

Go to bed often sounds slightly more idiomatic in everyday English if the idea is simply that the person is done for the night.
Go to sleep is also correct and can sound a bit more directly focused on sleeping itself.

So the Russian sentence is straightforward, natural, and conversational:

• Я допью чай и пойду спать. = I’ll finish my tea and go to bed.