Svako jutro stavljam podsjetnik u kalendar.

Because jutro is a neuter singular noun, and svako has to agree with it in gender, number, and case.

• svaki = masculine singular
• svaka = feminine singular
• svako = neuter singular

So:

• svaki dan = every day
• svaka večer = every evening
• svako jutro = every morning

It is in the accusative singular, used adverbially to express time when something happens regularly.

In Croatian, expressions like every day, every morning, every week are often built this way:

• svaki dan
• svaku večer
• svako jutro

So here svako jutro functions like an adverbial phrase meaning every morning.

Because this sentence describes a habitual, repeated action, and Croatian normally uses the imperfective verb for that.

• stavljati = imperfective, repeated/ongoing action
• staviti = perfective, completed single action

So:

• Svako jutro stavljam... = I put / I add / I set ... every morning
  habitual, repeated

If you used stavim, it would sound more like a completed one-time action or something with a future/result-oriented sense, not the normal way to describe a routine.

The infinitive is stavljati.

stavljam is:

• 1st person singular
• present tense

So it literally means I put / I am putting, but in this sentence it is best understood as I put in the sense of a routine.

Podsjetnik is the direct object, so it is in the accusative. But because it is a masculine inanimate noun, its accusative singular is the same as the nominative singular.

So:

• nominative: podsjetnik
• accusative: podsjetnik

That is normal for masculine inanimate nouns in Croatian.

Compare:

• vidim stol = I see a table
• stavljam podsjetnik = I put/set a reminder

But for masculine animate nouns, the accusative would usually change form.

Because Croatian uses different cases after u depending on whether the meaning is movement or location.

• u + accusative = into, to, movement toward the inside
• u + locative = in, inside, location

Here the verb stavljam implies putting something into the calendar, so Croatian uses accusative:

• u kalendar

Compare:

• Stavljam podsjetnik u kalendar. = I am putting a reminder into the calendar.
• Podsjetnik je u kalendaru. = The reminder is in the calendar.

Yes. It can be used for both a physical calendar and a digital one.

Croatian commonly uses u kalendar for the idea of adding something to a calendar in general, regardless of whether it is on paper or on a phone/computer.

Croatian word order is fairly flexible, and it is very common to put a time expression near the beginning.

So Svako jutro stavljam podsjetnik u kalendar sounds natural and neutral.

You could also say:

• Stavljam podsjetnik u kalendar svako jutro.

That is still grammatical, but it places the time phrase later and may sound slightly different in focus or rhythm.

Croatian has no articles like a/an or the.

So podsjetnik can mean:

• a reminder
• the reminder

The exact meaning depends on context.

In a sentence like this, English often translates it as a reminder, because it sounds like a general routine, but Croatian itself does not mark that distinction with an article.

No, but it is a natural and understandable way.

Depending on context, Croatian speakers might also say:

• dodajem podsjetnik u kalendar = I add a reminder to the calendar
• postavljam podsjetnik = I set a reminder
• upisujem podsjetnik u kalendar = I enter/write a reminder into the calendar

The best choice depends a bit on whether you mean physically writing something down, adding an event, or setting a phone reminder. But stavljam podsjetnik u kalendar is perfectly normal.

Yes. Croatian present tense often covers both meanings.

So stavljam can mean:

• I put (habitually, regularly)
• I am putting (right now)

In this sentence, because of svako jutro, the habitual meaning is the important one: I put / I set a reminder every morning.

Yes. Jutro is a neuter noun meaning morning, and in expressions of repeated time it often appears in phrases like:

• svako jutro = every morning
• jedno jutro = one morning
• cijelo jutro = all morning

So it behaves very naturally in these time expressions, and learning svako jutro as a fixed chunk is a good idea.