So I haven't yet seen solid evidence of a time frame, but I suspect its at least another five years. I have seen theories suggesting before it all happened, but I don't think we would see something that is supposed to be choice heavy with the Institute happen before Fallout 3. Also we are seeing the Brother active in the area, and there was little mention of them in Boston or Mass. during Fallout 3 (besides them going to Pittsburgh, a neighbor).

It could take place during the same time since New Vegas is so far away.

New Vegas is pretty much on the other side of the country, meanwhile Fallout 4 takes place on the east coast. It could be possible that Fallout 4 plays before or inbetween FNV and F3

I suspect Fallout 4 might take place sometime around the Fallout 3 afterword originally printed in the Fallout 3 game guide.

So 20 years after Fo3, and like 17? after NV.

Pretty sure Bethesda have said all their games will take place after the previous game. So it's post NV, however there's no ending I can see that would impact the east coast outside of a decades time difference, but I don't see that being the time span.

But Bethesda didn't make Fallout New Vegas, and I think that Fallout New Vegas wasn't from the main game series, it was more of a spin-off, If I'm not mistaken

I imagine we will find out soon enough. Personally post NV would be great. Maybe we could see the repercussions of those actions? MIT is very popular. I'd imagine SOMEONE would have heard about it over there? Which as a counter-argument, they have better things to be doing on the West-Coast I guess. My courier is currently embroiled with the after effects of his independence haha.

I figure Fallout 4 is going to take place somewhere between October of 2077 and 3:29 PM, June 6, 4728.

Beyond that I am not willing to speculate.

I like to think of F1/2/NV and Fallout 3/4 as parallel stories.

Bethesda wanted to make a world of their own within the Fallout Universe. Some might argue the West Coast is the main storyline and Tactics/Brotherhood East Coast is the spinoff, some might say West Coast WAS the main but now East Coast is and NV was the Ali off. I just like to think of them as parallel. Perhaps at some point, when I'm an even more bitter old man, the two will intersect and we'll have one comprehensive world.

i thought i heard somewhere it was rumored to take place ten years after fallout 3? maybe in the leaks? Either way seems as reasonable a guess as any