I am going to see my doctor, so I will be late for work.
あらかじめ伝えておかないといけないような通院(毎週○曜日とか)であれば、regular appointments を使いますが、朝起きて調子が悪いので、「[病院](https://eikaiwa.dmm.com/uknow/questions/32103/)行ってから会社行きます」程度の連絡であれば、I am going to see my doctor. (see a doctor も可) でいいと思います。
「～に[遅刻](https://eikaiwa.dmm.com/uknow/questions/42475/)します」は、be late for ～ (school, work, the meetingなど)です。
I have my regular doctor's appointment so I'll be a little late for work.
I have my check up at the doctor's, so I'll be late for work.
「通院」は"regular doctor's appointment" ということで、「普段の[お医者さん](https://eikaiwa.dmm.com/uknow/questions/52592/)のアポがある」という意味になります。
また、二つ目の"I have my check up at the doctor's"ということで、「通院」という意味になります。"check up" は「診てもらう」をかなりカジュアルに表現したものです。
I will be coming later to work tomorrow, I have a doctors appointment.
I will be late for work tomorrow, I must go for my monthly doctor's check up.
>I will be coming later to work tomorrow, I have a doctors appointment.
This sentence explain that you will be coming to work, but you will be late because you have a doctors appointment.
>I will be late for work tomorrow, I must go for my monthly doctor's check up.
This is telling them directly that you will be late for work and giving them the reason why.
I will be coming later to work tomorrow, I have a doctors appointment.
通院のために、仕事に遅れるということを意味しています。
I will be late for work tomorrow, I must go for my monthly doctor's check up.
仕事に遅れる理由を直接的に言う表現です。
I'll be late for work due to a routine doctor's appointment
Routine - if something is 'routine' it m,eans that it is normal, part of everyday life, unchanged from the usual way of doing something or behaving
"I've got a routine job with a local company."
"I will be late.." Here you are advising the listener of the inevitability that you will not be arriving at work on time,
"Routine"（日課となている事）
- 何か'routine'があるとしたらそれはいつもの日課で毎日変わることなく行われる習慣と言う意味になります。
【例】
"I've got a routine job with a local company."
（地元の会社でお決まりの仕事があります）
"I will be late."
（遅れてしまいます）
この表現を使って仕事に遅れてしまう事を伝えることが出来ます。
I'll be a little late due to my regular doctor's appointment
I'll be late due to my regular doctor's appointment
It's important to mention that it is a 'regular' appointment, as this explains that it will happen on more than one occasion. You can say a 'little late' if you won't be more than one hour late. If you will be more than an hour late, just say "I'll be late".
これは一回だけではなく'regular'（定期的な）通院であることを説明することがとても大事です。
もし、1時間以上遅れる場合で無ければ'little late'（少し遅れる）と言う事が出来ます。
1時間以上遅れる場合はただ "I'll be late"（遅れます）と言いましょう。
Im sorry, I am going to be late as I have a scheduled outpatients appointment with my GP
I have a doctors appointment so I am going to be late.
I have an outpatients appointment so I will be late to work
A regular doctors appointment could be referred to as a scheduled appointment. You could let your place of work know that you are going to be late because of this appointment by using one of the sentences above.
Hope this helps
Teacher Jemxii
I will be late for work tomorrow, due to attending my routine doctors appointment...
A deviation from normal behaviour is usually, "due to something" ( IE caused by!)
in this case we need to explain we will not be on time ...Due to a doctors appointment!
"I will be late for work tomorrow, due to attending my routine doctors appointment..."
何かしらで（due to something）、普段の行動が変わることはよくあります
この場合は、（医者の予約で）遅れることを説明しないといけません。
"I will be late for work tomorrow, due to attending my routine doctors appointment..."
明日、通院の予約があるため、仕事に遅れます。
I'm going to be late because I have a doctor's appointment.
例えば下記のような英語表現はいかがでしょうか：
・I'm going to be late because I have a doctor's appointment.
病院に行かなければいけないので遅れます。
doctor's appointment は直訳すると「医者の予約・予定」というニュアンスを持つ英語表現です。
シンプルですが使いやすい英語フレーズだと思います。
お役に立てれば嬉しいです。
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