This year (2016), the Biblical date for Passover (The Feast of Unleavened Bread) will begin Saturday night April 23, 2016 at sunset until Saturday night April 30 at sunset.
There are several issues that are confusing many people. The first confusion has to do with how to begin the Hebrew month. In 359 CE (AD), the Romans abolished the Sanhedrin and a Rabbi named Hillel II replaced the Biblical calendar with a calculated one. Up until 359, the Sanhedrin (actually a court of three appointed by them) would interview new moon witnesses who sighted the new moon every month. With the Sanhedrin abolished, Hillel II swapped out the visible new moon for conjunction also called the "dark moon". In the 4th century, it was relatively easy to calculate conjunction but impossible to calculate visibility, so Hillel settled for what he could do with the state of technology at the time. However, rabbis ever since have proclaimed that when the Messiah comes and reestablishes the Sanhedrin, they will go back to sighting the new moon.
Today most Jews observe the calendar of Hillel II based on conjunction, while many Karaite Jews continue the pre-Hillel system of sighting the New Moon. Based on Hillel II's calculation, Passover would be Friday night April 22, but based on the actual visible New Moon it should really be Saturday night April 23. I prefer to celebrate according to what King David would do and not Hillel II, even if it means I'm a day off from 99.99% of my Jewish brothers and sisters.
If that wasn't complicated enough, there is the issue of how to begin the new Hebrew year. Biblically, we are commanded in Deuteronomy 16:1 "Observe the month of the Aviv". Hillel II replaced this with an approximate calculation, which just happened to get the month right this year (even if it's one day off). However, some Christian and Messianic groups will be observing Passover based on other considerations. I wrote a piece about this recently, which you can read here.
I want to honor those who are observing Passover at a different time for at least striving for Biblical truth. They deserve credit for making an effort and not blindly following what others say, even if in my humble opinion they are in error.
If you aren't confused yet, I need to throw in one more complication and that has to do with the definition of the word "Passover". In every language, the meanings of words change over times. A great example in English is the word "computer". In the 1910s the English word "computer" referred to a person (usually a woman) whose job it was to sit with a pen, paper, and a slide rule computing complex calculations for banks, astronomers, and the military. A hundred years later "computer" refers to an inanimate machine that does everything from taking photographs to running the word processor on which I am writing this message. In the Torah, Pessach or "Passover" refers to a sacrifice and the holiday is called Chag HaMatzot (Feast of Unleavened Bread). However, in late Second Temple times the name "Passover" took on a new meaning and was used to refer not only to the sacrifice, but to the holiday that followed the sacrifice. If you said to King David you are "doing Pessach" he would know you are offering a sacrifice. If you said the same thing to a 1st century CE Jew, he might think you were observing the Feast of Unleavened Bread or maybe offering a sacrifice. He wouldn't know and might have to ask you. If you said to most Jews today you are "doing Pessach" they would immediately know you meant the Feast of Unleavened Bread and not a sacrifice.
The Feast of Unleavened Bread is a 7-day holiday that begins on the 15th day of the First Hebrew Month and continues until sunset on the 21st day of the First Hebrew month. This year that coincides on the Biblical calendar with sunset April 23 through sunset April 30. The Torah says the Passover sacrifice itself was brought at the end of the 14th day of the First Hebrew month, which this year would be late afternoon on April 23, 2016 according to the Biblical calendar. Of course, we don't have a Temple today so according to Deuteronomy 16:5 we can't bring the Passover sacrifice, we can only commemorate it. However, we still can observe the Feast of Unleavened Bread.
The confusion comes from some 19th Century German Bible scholars headed by Julius Wellhausen who wanted to separate the Passover sacrifice from the Feast of Unleavened Bread. They claimed that the Passover was originally sacrificed at the beginning of the 14th day of the First Hebrew month rather than at the end. They didn't have a shred of historical proof. No Jewish group ever observed the Passover sacrifice this way. However, it fit in with their beliefs about the Torah being compiled from four different "documents". This was part of a larger Anti-Semitic doctrine aimed at separating "The Jews" from "Israel". To do this, they picked out the parts of the Torah they liked and attributed them to "Israel" whereas the parts they didn't like were assigned to "The Jews". "Passover" was Israelite whereas the "Feast of Unleavened Bread" was a later Jewish invention. The overall theory is sometimes referred to as the "Documentary Hypothesis".
Unfortunately, this Anti-Semitic doctrine is the basis of so-called "Higher Criticism" of the Torah taught in most secular universities and liberal seminaries. I was even taught this at the Hebrew University of Jerusalem where they admitted its Anti-Semitic, origins but still taught it as truth! Decades ago Herbert Armstrong accepted this "scholarly" theory without understanding its origins and broader ramifications. As a result, he taught that Passover (or a commemoration of it) was to be observed as a separate event from the Feast of Unleavened Bread. This is why some Messianic groups are "doing Passover" on April 22, but then beginning the Feast of Unleavened Bread a day later. I prefer to stick with what King David did. He was both an Israelite and a Jew and if it was good enough for him, it's good enough for me.
I know this is a lot to follow and may be confusing to some people who are new to all this and even to some who are old to it. Here's the bottom line: If you want to follow the Biblical calendar, then the Feast of Unleavened Bread is sunset April 23 through sunset April 30, 2016. The Passover would have been brought if there were a Temple late in the afternoon on April 23, 2016, but today Jews don't bring this sacrifice outside the Temple. They do commemorate it by telling over the story of the Exodus. I'll be doing my telling-over on April 23, 2016 at sunset.
Whether you are keeping the Biblical calendar, the Hillel II calendar, or some other calendar, I want to wish you a happy and healthy Chag HaMatzot!
Enjoy this music video from the Maccabeats who sing a Passover version of Les Miserables!