予定だ【よていだ】

予定だ says that something is planned or scheduled: the arrangement has already been made. A verb goes in the dictionary form, or the ない-form for a plan not to do something, with nothing between it and よてい予定. In polite speech it is よてい予定です.

• × 行くの予定です → 行く予定です

After a noun, の goes in between.

予定 or つもり

つもり is what you yourself intend to do. 予定 is what has been arranged – a timetable, a booking, a decision – so it works for trains, meetings and other people as well as for you.

A train cannot intend anything: ×電車は5時に着くつもりです.

予定だった

The past, よてい予定だった or よてい予定でした, says what was supposed to happen, and usually that it didn't.

The verb before 予定 stays in the dictionary form here too: ×会った予定だった.