Best Scenario?
250M OW 40% drop 150M Second Weekend 50% drop 60M Third Weekend 60% drop 24M Fourth Weekend
250 + 150 + 60 + 24 = 484 From Weekends + around 150 to 200 (total gross, not only the 4 weeks cycle) from Weekdays for final 634-684M
Worst?
220M OW
60% Drop 88M Second Weekend
60% Drop 35M Third Weekend
60% Drop 14M Fourth Weekend
220+88+35+14 = 357 From Weekends + around 150 to 200 from weekdays (total gross, not only the 4 weeks cycle) for final 507-557M
The Avengers made ~110M from Weekdays (May 7th to May 24th)
Age of Ultron made ~75M from Weekdays (May 4th - May 21st)
Civil War made ~72.5M from Weekdays (May 9th - May 26th)
Black Panther made ~141M From Weekdays (Feb 19th - March 8th)
Now I'm only predicting till IW 4th weekend but adding low-balled total Weekday gross(not only 4 weeks gross).
Neither Ultron or Civil War had drop bigger than 60% for the 4th weekends cycle.
Worst Scenario:
With TA Weekdays money - 357 + 110 = 467M By May 20th
With Ultron Weekdays money - 357 + 75 = 432M By May 20th
With Civil War Weekdays money - 357 + 72.5 = 429.5M by May 20th
With Black Panther Weekdays money - 357 + 141 = 498M by May 20th
Best Scenario:
With TA Weekdays money - 484 + 110 = 594M By May 20th
With Ultron Weekdays money - 484 + 75 = 559M By May 20th
With Civil War Weekdays money - 484 + 72.5 = 556.5M by May 20th
With Black Panther Weekdays money - 484 + 141 = 625M by May 20th
To sum it up - I'm using IW Gross using only 4th weekends and the 4 weeks, weekdays gross of the other MCU movies
I think IW is pretty much 500M safe.