I would like to know if there are reputable sources presenting anything close to an exhaustive listing of the main denominations around the world adhering to seventh-day Sabbatarianism. Similarly, are there recent studies estimating the percentage of Christendom that practices seventh-day Sabbatarianism?
2 Answers
By far the largest seventh day sabbatarian churches are the Seventh Day Adventist church which has approximately 21 million members, and the Seventh Day Baptist churches with approximately 50,000 members worldwide.
This means they represent about 1% of Christians
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"By far the largest seventh day sabbatarian churches are [...] " drawing on my common sense I'm biased to agree, but a reputable source backing up this claim would certainly be helpful.– user50422Oct 12, 2020 at 1:07
Straight from the churches main website: Seventh-day Adventist World Church Statistics 2018.
And some other data that will get more granular: Browse by Adventist World Divisions.
This is limited to the Seventh-day Adventist numbers, but they are the largest group of Sabbatarians.