When does the great tribulation Jesus describes in Matthew 24:21 begin?

Its beginning is fixed at the midpoint of the Tribulation, with the event Jesus has just described, when the escaping remnant of Jews must flee. From then the final three and a half years become the most awful time in human history, unequaled before or afterward.

Les explains that Matthew 24:21 opens with “For then,” tying the great tribulation to the midpoint of the Tribulation. The preceding instructions about fleeing Judea and praying it not be winter or on the Sabbath introduce that same event. From this midpoint, the last three and a half years will be the most awful time in all human history, beyond imagination. This escaping group of Jews then goes to their place in the wilderness, where the triune God protects and feeds them, while the dragon, Satan, persecutes the woman, Israel.

Matthew 24:21

For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.

Where else does the Bible describe the great tribulation in Revelation?

The great tribulation is also described in the book of Revelation, specifically through the trumpet judgments and the bowl judgments. These judgments depict the same period of great tribulation that Jesus spoke of in Matthew 24:21. The context connects them as end-time events.