Okay what is this doomsday Mayan calendar prediction On June 21 2020 where did it come from?

there isn't one.  It is BS

It came from "The Sun", a British tabloid that enjoys sensationalism - while not always caring about the truth.
They were quoting a self-acclaimed prophet (Paolo Tagaloguin) who claimed that we are really in the year 2012 according to the Julian calendar (which is totally false, as the Julian calendar is only 15 days different from our Gregorian calendar).
Turned out so bad an article that even The Sun removed it from their web site.

It is simply a rerun of the December 21, 2012 "Mayan" end-of-the-world.
Of course, the Mayan themselves have nothing to do with it.
Although the Mayan civilization is not as powerfull as they once were, there are still Mayan people out there who know what their real culture says. And they were already laughing at the idiots who made up this doomsday stuff back in the 2010's.

There is absolutely NO doomsday prediction in the Mayan calendar. This one (like all the other ones) is just like if you went around saying "My wall calendar ends on December 31. Does that mean the world will end?"

The popularity of the hoax increased dramatically when Roland Emerich used it in the promotion of his movie "2012" (the plot of the movie was actually based on another hoax: the end of the world of May 2003, caused by Planet-X).

More Internet BS.  Remember the Mayan calendar prediction about the end of the world in 2012?  Did you notice anything different?

You're about 8 years too late.

Its the same nutjobs that brought you the EOTW in 2012.

They forget the part about "calendar continued on next rock."

I thought the world ended in 2012. 

One of the cycles in the Maya calendar is the "Long Count", totaling 5125 years. The previous cycle started in 3114 BC and ended in 2012 AD. It's just a dating system and when one cycle is finished the calendar starts over.

The calendar is strange enough that someone inclined to believe ancient people possessed the lost knowledge of ancient astronauts (etc.) might interpret it as the foretelling of the end of the world. Since we managed to get through 2012 unscathed, these same types would be inclined to run the numbers again to see where they went wrong.

They pulled it out of their butts.
Just like all the other predictions before it.
http://www.abhota.info/end1.htm

It came from the fat behinds of morons and only other morons believe a word of it.

Nonsense, just something to gather attention for the lonely.

Dec 21 is the winter solstice, the shortest day (around 10 hours) and the longest night (about 14 hours depending upon where you live). There is a really cool program called Moonrise that uses your longitude and latitude to provide sunset, sunrise, moonset and moonrise and moon phases for your location. The calendar only tracks the earth's cyclical journey around our star. An "end of the world" doesn't make any sense based upon this cycle.  Suppose our galaxy or solar system is moving in some grand orbit destined to collide with the edge of the universe? The calendar cycle doesn't include that information. It would be easy for "holy" men to con the gullible after accurately predicting cyclical phases. I bet that is what happened. 

It's because the Mayan calendar stopped at 2012 your 8 years too late

With link the corona virus pandemic stupidity will be done by then 

I thought it ended in 2012...? 
2020 must be the next page - er, rock - of the calendar...

I lived through so many ends of the world - probably a dozen - I'm beginning to think perhaps they might not all be true.

https://www.google.com/amp/s/zeenews.india.com/world/mayan-calendar-was-wrong-and-world-will-end-next-week-on-june-21-warns-conspiracy-theorist-2289849.html/amp... 

Basically, another internet hoax just like all the other 'end of the world' predictions I've seen here.

The Mayan Calendar, b*tch 

The world has ended many times, and each time it seems to get better. When steam trains were replaced by diesel, when electricity was invented, the advent of Radio, then telephone, Aircraft, Steel and concrete. These are all things that changed the world.

They carved the calendar out of stone and they could only carve out so much so they must have stopped at 6/21/2020. Or we have 4 days to live.

The world ended in 2012 when the Mayan calendar Long Count came to an end back then.  Weren't you paying attention?

I suspect  that every day ,of every year ,has been predicted to be doomsday ,at sometime or other . 

One day you are going to die -- and on that day ,my prediction will come true .

Gee , I'm good .

been around for a thousand years, so nothing to worry about ............