Since late in the 19th century, they had taught that the "battle of the Great Day of God Almighty" (Armageddon) would happen in 1914 CE. It didn't.
The next major estimate was 1925. Watchtower magazine predicted: "The year 1925 is a date definitely and clearly marked in the Scriptures, even more clearly than that of 1914; but it would be presumptuous on the part of any faithful follower of the Lord to assume just what the Lord is going to do during that year." 6
The Watchtower Society selected 1975 as its next main prediction. This was based on the estimate "according to reliable Bible chronology Adam was created in the year 4026 BCE, likely in the autumn of the year, at the end of the sixth day of creation." 8 They believed that the year 1975 a promising date for the end of the world, as it was the 6,000th anniversary of Adam's creation. Exactly 1,000 years was to pass for each day of the creation week. This prophecy also failed.
The current estimate is that the end of the world as we know it will happen precisely 6000 years after the creation of Eve. 9 There is no way of knowing when this happened.