Is there any big difference between these two sentences: We will have been married for 25 years by friday/ on friday
We will be married for 25 years by friday/ on friday?
Is there any big difference between these two sentences: We will have been married for 25 years by friday/ on friday
We will be married for 25 years by friday/ on friday?
The coupled is already married.
[1] We will have been married for 25 years by friday/ on friday.
[2] We will be married for 25 years by friday/ on friday.
[1] has the auxiliary verb pair have been. The sentence hence conveys correctly that
we are married, and the marriage will be reaching its 25th anniversary this friday.
[2] says will be married. It hence does not convey the fact as accurately. Although the 25 years should clear any doubts, the sentence is just less sound. As what @FumbleFingers says, this is stylistically poor.
When a couple celebrates twenty-fives of marriage it means the marriage ceremony was performed at a specific date in the past, and this state of being married is ongoing until something happens which interrupts this union.
When we want to express an action that began in the past and continues to the present day we use the Present Perfect.
We have been married for 25 years. ✅
When we want to say a certain event will be completed before or at a specific point in the future, we can use the Future Perfect
We will have been married 25 years by Friday. ✅
Note that days of the week in English are always capitalised, and the omission of preposition "for" is facultative here.
The OP's second sentence is awkward, it would probably be marked incorrect in an English test or exam.
We will be married for 25 years by friday/ on friday?
The Future Simple has many functions and uses: planned events/actions, expressing opinions about future events and also stating facts among others.
We'll fly to Dublin next Friday.
The train to Manchester will leave at 09.45.
I'm sure he'll pass his driving test on Friday.
Christmas Day will fall on a Monday this year.
We will be married for 25 years this/in June.
The preposition "by" in "by Friday" means no later than. It would be correct to say: