По истечении месяца автопродление закончится.

По истечении is a set expression meaning after the expiration of, after the end of, or more naturally once ... has elapsed.

So по истечении месяца means after a month has passed or when the month is over.

This expression is fairly formal and is especially common in:

• contracts
• subscription terms
• legal or bureaucratic language
• official notices

It sounds more formal than everyday options like через месяц.

Because по истечении requires the genitive case.

• месяц = nominative
• месяца = genitive

So:

• по истечении месяца = after the expiration of a month

This is something you largely have to learn as part of the whole expression. It is best to memorize по истечении + genitive as a fixed pattern.

They are similar, but not identical in tone or emphasis.

• через месяц usually means in a month / one month from now
• по истечении месяца means after the month has fully elapsed

In many contexts they point to the same time, but по истечении месяца sounds:

• more formal
• more precise
• more typical of legal or service-related wording

So if this is a sentence about a subscription or automatic renewal, по истечении месяца fits very well.

Автопродление means automatic renewal or auto-renewal.

It is formed from:

• авто- = auto-
• продление = renewal / extension

The base noun продление comes from the verb продлить (to extend / renew).

This kind of compact noun is very common in modern Russian, especially in tech, subscriptions, and services.

Because продление is a neuter noun, and автопродление keeps that gender.

Most Russian nouns ending in -ение are neuter:

• решение
• движение
• сообщение
• продление

That is why the verb is закончится, the 3rd person singular form agreeing with a neuter singular subject:

• автопродление закончится

Закончится is the perfective future form, meaning will end.

Compare:

• заканчивается = is ending / ends (imperfective, present)
• закончится = will end / will come to an end (perfective future)

Since the sentence refers to a future point — after the month has elapsed — Russian uses the future form:

• автопродление закончится = the auto-renewal will end

The perfective verb focuses on the completed result: the renewal will stop.

The -ся marks the verb as reflexive, but in many cases Russian reflexive verbs are not literally reflexive in the English sense.

Here закончиться means to come to an end, to end, or to finish.

Compare:

• закончить что-то = to finish something
• закончиться = to end / to finish

So:

• Компания закончила акцию = The company ended the promotion
• Акция закончилась = The promotion ended

In your sentence, автопродление is the thing that comes to an end by itself, so закончится is the correct form.

The subject is автопродление.

You can tell because:

• it is in the nominative case
• the verb agrees with it in number and person

So the structure is basically:

• По истечении месяца = time expression
• автопродление = subject
• закончится = predicate

A natural parsing is: After a month has elapsed, the auto-renewal will end.

No, Russian word order is flexible, but the original order is very natural.

По истечении месяца автопродление закончится sounds like:

1. first, set the time frame
2. then state what will happen

You could also say:

• Автопродление закончится по истечении месяца

That version is also grammatical, but it puts slightly more focus on автопродление закончится and sounds a bit less like standard official wording.

In notices, instructions, or policy text, the original order is very typical.

Yes, it is natural, especially in formal or service-related contexts.

That said, there are other possible phrasings depending on style:

• Через месяц автопродление прекратится.
• Автопродление закончится через месяц.
• По истечении месяца автоматическое продление прекратится.

Differences:

• автопродление is shorter and common in modern service language
• автоматическое продление is more explicit
• прекратится can sound slightly more formal or technical than закончится

So your original sentence is perfectly fine, especially for a website, subscription message, or contract-like text.

Not necessarily.

Usually по истечении месяца means after one month has elapsed, not specifically at the end of the calendar month.

So if something starts on the 10th, this phrase often implies the relevant point is reached one month later, not automatically on the 30th or 31st.

If someone wanted to say at the end of the calendar month, Russian would more likely use something like:

• в конце месяца
• по окончании месяца in some contexts

So the exact interpretation depends on the broader context, but by itself по истечении месяца usually means once a month-long period has passed.