There are five viewpoints on the tribulation:
Pre-Tribulation
Meaning all Saints alive at the time the tribulation begins will be taken up bodily to meet Christ in the clouds and subsequently go to Heaven. This is referred to as the Rapture or the First Advent of Christ (1 Thess. 4:13-18; 1 Cor. 15:50-55). Those who become believers after the tribulation begins, do so by refusing the mark of the beast and being killed off (Rev 13:15-18). The only biblical support is for the Pre Tribulation.
Pre-Wrath Tribulation
Meaning the Rapture will occur during the Tribulation at the Midpoint but before the Seven Vial Judgments.
Seven Trumpet Tribulation
The Rapture occurs at the sound of the seventh trumpet (Rev 11:15; 1 Cor. 15:52)
Mid-Tribulation
Rapture occurs at the 31⁄2 year point, before the harsher aspects of the tribulation unfold.
Post-Tribulation
No one is taken to Heaven at all. Everyone is gathered on Earth by Christ into the thousand year reign at the end of the tribulation.