When do we use Future Perfect?
For actions completed before a future moment
Future Perfect describes an action that will be COMPLETED before a specific moment in the future. You are looking back from a future point and saying "by then, this will be done".
Something will be finished before a specific future time.
By tomorrow, Eva will have finished building the robot.
"by tomorrow" = before tomorrow
By 5 pm, I will have completed all my work.
"by 5 pm" = before 5 pm
By the time you arrive, I will have cooked dinner.
"by the time" = before you arrive
Imagine yourself at a future moment and describe what will already be done.
By next year, I will have graduated from school.
looking back from next year
By the time I am 30, I will have started my own company.
looking back from age 30
Future Perfect = completed BEFORE a future moment. Future Simple = will happen AT a future moment. "By 5 pm, I will have finished." (done before 5 pm) vs "At 5 pm, I will finish." (happening at 5 pm)