In some situations, you can use last and past interchangeably with no difference in
meaning:
▶️ The economy has improved in the past month.
▶️ The economy has improved in the last month.
When used with time, the word past always requires the or this – but the word last
does not.
▶️ Last weekend I went to the beach.
▶️ This past weekend I went to the beach.
Past weekend I went to the beach.
▶️ I started a new job last year.
I started a new job past year.
▶️ I’ve been very busy the last few days.
= I’ve been very busy the past few days.
▶️ The company has hired several new people in the past month.
= The company has hired several new people in the last month.
There is also a difference between “last year” and “in the last/past year.”
▶️ If it is September of 2014…
o “last year” means the year 2013 (January – December)
o “in the last/past year” means “in the most recent 12 months up to now: