In reply to a question form Janet:

Thanks for your question about why Pentecost / The Feast of Weeks / Shavuot is occurring on June 16th in this year of 2019.
First, Leviticus 23:9-11 tells us the day of the wave sheaf offering was to be on the day after the Sabbath during the days of unleavened bread.  The Sabbath being the 7th day of the week, and “the day after the Sabbath” being  the 1st day of the week (which starts at sundown on Saturday night).   That is the time that you start counting, to the day after the 7 weeks (or 50 days).
Remember, “the day after the Sabbath” (the 1st day) must be during or within the days of unleavened bread.  Sometimes the Sabbath used to determine the wave sheaf day is also within the days of unleavened bread, but sometimes it’s not!  This difference has caused confusion for many.    This is especially important when the Sabbath is close to Passover.  For instance, the year that the Israelites entered the promised land, Joshua 5:10-12 tells us that year, the Passover was on a Sabbath, and the next day they ate the produce of the land.   In order to do that, they would have had to perform the wave sheaf offering on or before that day as required by Leviticus 23:14.  And since that year, that day happened to be the first day of Unleavened bread, they were required to do the wave sheaf offering on that day in order to eat that produce or parched grain, etc.
So, when we have a Passover on the Sabbath, then the next day is the wave sheaf offering as we’ve just seen. However, if the Passover is on a Sunday (or later), like it was this year, then you have to wait until the “following” Sabbath.   The reason for this is that first day of the week here was the Passover, and it is NOT during the days of Unleavened Bread as defined by Leviticus 23:5-6.
If you count the 7 weeks from the evening after the Sabbath (Saturday Night) on April 27th, you will end up at the end of the Sabbath, on June 15th, and the day after is the 50th day, which is June 16th. 
Of course, different people with different calendars, especially people who are on the calculated calendar or who follow conjunction will be a day or two earlier.  This means that this year, since Passover was on or before the Sabbath of April 20th for them, the first day of the week during the days of unleavened bread was on April 21st for them.  This therefore also means that their Pentecost calculation ends up a week earlier as well on June 9th.
So, that is why June 16th is Pentecost / Shavuot in this year of 2019.  Hope this helps.