Although April is a significant month for the LDS Church — General Conference is the first weekend; Joseph Smith organized the Church on April 6, 1830, and Easter usually falls in April (sometimes March) — the belief that Christ was born on April 6 is questionable. I know, I know, I have heard it from the stand, from apostles, maybe even a prophet or two. (Harold B. Lee, Spencer W. Kimball)
I have often wondered about that scripture in the Doctrine and Covenants and thought it might refer only to the date the church was established, not the date of our Savior’s birthday. Supposedly, there was no official church stance on the date. But…I had heard it often.
The history behind the April 6 belief
James Talmage, an apostle, wrote a book called Jesus The Christ, in 1915 where he stated that Jesus Christ was born on April 6, 1 BC. [I wonder if this was how he stated it in the original edition as well as the more current ones.] This was/are a much-acclaimed book and one of the books the church recommends to all missionaries. Talmage wrote the book in the Salt Lake Temple, which seemed to give more validity to his writings — assuming it was all revelation. However, there were other opinions. The apostle, J.Reuben Clark, a member of the First Presidency in 1954, wrote that Jesus was born  December 5 BC or 4 BC. Bruce McConkie in his book, Mortal Messiah stated in 1979,
We do not believe it is possible with the present state of our knowledge-including that which is known both in and out of the Church-to state with finality when the natal day of the Lord Jesus actually occurred” (Vol. 1, p. 349, n. 2).
The scripture that James Talmage based his belief on was D&C 20:1, which refers to the date that the LDS church was organized.
The rise of The Church of Christ in these last days, being one thousand eight hundred and thirty years since the coming of our Lord and Savior Jesus Christ in the flesh, it (the church) being regularly organized and established agreeable to the laws of our country, by the will and commandments of God, in the fourth month, and on the sixth day of the month which is called April. (D&C 20:1)
Many of us had read that scripture as if the Lord were speaking directly to Joseph and revealing that Christ was born exactly 1,830 years before that exact date the church was organized: April 6.
The Heading to the Revelation written by John Whitmer
However, that statement is actually a heading written by John Whitmer, Joseph Smith’s scribe, who often wrote an introductory to the actual revelation. According to the newer information being examined in the Joseph Smith Papers Project, and volume editor, Steven C. Harper, assistant professor of church history at BYU. Oh, and by-the-way, the date Whitmer wrote the heading was April 10, not April 6.
There are several other times when John Whitmer wrote this 19th Century way of referring to the year:
“It is now June the twelfth, one thousand eight hundred and thirty one years, since the coming of our Lord and Savior in the flesh.”
It appears that D&C 20:1 is the introduction of D&C 20, and we should not read it as a revelation from God as to the birthdate of Jesus. John Whitmer wrote it as a heading.
Some say April; some say December.
Another BYU professor, Jeffrey R. Chadwick, Jerusalem Center Professor of Archeology and Near Eastern Studies, published his research in BYU Studies in an article titled: “Dating the Birth of Jesus Christ,” which also challenges the April 6th date. Looking at all the research and documents available (which he lists in the article), Professor Chadwick narrows the date down to December of 5 BC as the probable date of the Savior.
Others believe that Christ was born in April for other reasons. I read an article by John Tvedtnes — “When Was Christ Born?”  Tvedtnes believes that Christ was born in April and gives some possible reasons.
And others have left comments that offer good support for one or the other.
For Your Reading:
The Joseph Smith Papers, Articles and Covenants, 10 April 1830 [D&C 20] (searchable online–read the original manuscript as well)
The Joseph Smith Papers: The Manuscript Revelation Books (Ensign)
What was the Real Date of Jesus’ Birth? (Deseret News, Dec. 24, 2010)
When was Christ born? (Tvedtnes)
Dating the Birth of Christ (Chadwick)