Today is Monday. Monday is today.
Yesterday was Sunday. Sunday was yesterday.
Tomorrow is Tuesday. Tuesday is tomorrow.
This month is May. May is this month.
Last month was April. April was last month.
Next month is June. June is next month.
This year is 2025. 2025 is this year.
Last year was 2024. 2024 was last year.
Next year is 2026. 2026 is next year.
This decade is the Twenties. The Twenties is this decade.
Last decade was the Teens. The Teens was last decade.
Next decade is the Thirties. The Thirties is next decade.
This century is the 21st. The 21st is this century.
Last century was the 20th. The 20th was last century.
Next century is the 22nd. The 22nd is next century.
Now are you clear about when what is?