According to the original plan, it was supposed to be completed next month.
at first; initially; originally
Adverbial use meaning 'in the beginning' or 'at the outset', often contrasting with a later change or outcome.
当初は反対だったが、今は賛成だ。
I was against it at first, but now I'm in favor.
当初、この問題は軽視されていた。
Initially, this problem was underestimated.
According to the original schedule, it was supposed to be finished next month.
At first many people were opposed, but now more people are in favor.
This project had problems from the very beginning.