Lutheran demographer Lyman Stone wrote for the Institute of Family Studies today a fascinating article about fertility rates between religious groups.
His main takeaway is that the religious have much higher fertility rates:
But in the back half of his article, he discusses if the fertility rate of different religious groups is high enough to maintain stability. While Stone lumps Latter-day Saints in with many other groups, so doesn’t dig into his numbers in this article, but his article suggests that if current trends remain, Latter-day Saints should expect to see decreases between 10%-40%.