dallyeoge yaksok naljjareul jeogeo dueosseoyo.

달력에 means on the calendar.

The particle 에 is used because it marks the place where something is written. In Korean, when you write something in or on a place, 에 is commonly used.

For example:

• 공책에 적어요 = write it in a notebook
• 벽에 붙였어요 = attached it to the wall
• 달력에 적었어요 = wrote it on the calendar

So in this sentence, 달력에 tells you where the appointment date was written.

약속 날짜 literally means appointment date or the date of the appointment.

This is a noun-noun combination:

• 약속 = appointment, engagement, promise, plans
• 날짜 = date

So 약속 날짜를 적다 means to write down the date of the appointment.

In English, we often use of or a possessive idea, but in Korean, two nouns are often placed together directly:

• 시험 날짜 = test date
• 생일 날짜 = birthday date
• 회의 시간 = meeting time

를 is the object marker. It marks 날짜 as the thing being written down.

So:

• 달력에 = on the calendar
• 약속 날짜를 = the appointment date
• 적어 두었어요 = wrote it down and left it that way / have written it down

In other words, 날짜 is the direct object of 적다 (to write).

The base form is 적어 두다.

This is made from:

• 적다 = to write down
• 두다 = to put, leave

When -아/어 두다 is attached to a verb, it often means to do something in advance and leave it in that state for later convenience.

So 적어 두다 is not just to write, but more like:

• to write down and keep it there
• to write it down in advance
• to make a note of it

This is a very common question.

• 적었어요 = I wrote it down.
• 적어 두었어요 = I wrote it down and left it there for future use / I made a note of it.

The -아/어 두다 adds the idea of preparation or keeping something ready.

So if you say:

• 달력에 약속 날짜를 적었어요
  = I wrote the appointment date on the calendar.

• 달력에 약속 날짜를 적어 두었어요
  = I wrote the appointment date on the calendar so I wouldn’t forget it / so it would be there later.

That extra nuance is important.

Here, 두었어요 is the past form of 두다.

The sentence describes a completed action:

• the speaker already wrote the date down
• and it remains written there

So:

• 적어 두어요 = write it down and keep it there / write it down in advance
• 적어 두었어요 = wrote it down and kept it there / have written it down

You may also hear the contracted form:

• 적어 뒀어요

That is very common in speech and casual writing.

It can often sound similar in English, yes.

적어 두었어요 often implies:

• the action was completed earlier
• the result still matters now

So depending on context, it might be translated as:

• I wrote it down
• I’ve written it down
• I made a note of it
• I put it on the calendar

The exact English translation depends on what sounds most natural, but the Korean form emphasizes the lasting result.

The subject is omitted because Korean often leaves out subjects when they are understood from context.

So this sentence could mean:

• I wrote the appointment date on the calendar
• We wrote the appointment date on the calendar
• Someone wrote the appointment date on the calendar

In most everyday situations, the listener understands who the subject is from context. Very often, it would naturally be I.

Korean does this much more often than English.

Korean commonly links nouns directly together, where English often uses:

• of
• for
• possessives
• relative phrasing

So 약속 날짜 is a very normal Korean-style noun combination.

Other examples:

• 여행 계획 = travel plan
• 수업 시간 = class time
• 병원 예약 날짜 = hospital reservation date

English learners sometimes expect an extra word between the nouns, but Korean often does not need one.

Yes. 약속 can mean:

• promise
• appointment
• plans / engagement

Its exact meaning depends on context.

For example:

• 약속을 지키다 = keep a promise
• 친구와 약속이 있어요 = I have plans/an appointment with a friend
• 약속 날짜 = appointment date / date of the plan

In this sentence, because it is followed by 날짜, it clearly refers to a scheduled appointment or plan, not a promise in the moral sense.

It is in the -어요 / -아요 polite style, which is polite and commonly used in everyday conversation.

So:

• 적어 두었어요 = polite
• 적어 두었어 = casual/informal
• 적어 두었습니다 = more formal

This sentence is polite but natural, suitable for normal conversation.

In practice, both may be seen, but 적어 두었어요 is the standard spacing because 두다 is an auxiliary verb here and is often written separately.

However, in real life, many people also write it 붙여서 as:

• 적어두었어요

You may also see:

• 적어 뒀어요 in speech-like writing

For learning purposes, 적어 두었어요 is a very good form to remember.

Sometimes, yes, depending on context. But literally, 적다 means to write down, not specifically to mark.

So the most direct sense is:

• write down
• make a note of
• put down in writing

If the context is a calendar, natural English might sometimes say:

• I put the date on the calendar
• I wrote the appointment date on the calendar
• I noted the date on the calendar

So marked may work in some situations, but it is not the most literal choice.