In a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed.
1 Corinthians 15:52
This verse mentions the “last trumpet”. Some categorically connect this trumpet to the “seventh trumpet” in Revelation, but this is not Textual. In Revelation 11:15, it calls that trumpet the “seventh trumpet”, not the last trumpet.
Various difficulties arise when you attempt to equate these two trumpets. But, very simply, they are not claimed to be one and the same, and simply are not.
This idea might seem simple enough, but even in most chronologies of the book of Revelation, one has to admit that there are 7 bowls of wrath and and other things yet to come. The notion that this would be the last trumpet, therefore, seems a little far-fetched.
Rather, this trumpet would speak of the end of Revelation 20, at the Second Coming, the appearance of Jesus on His throne. This is presumably the second coming He talked about, with the glory of the Father and His Holy Angels, and this throne would be the throne of His Glory.
With a Millennium already past us now (see here for that explanation), the state is now set for the Gog Magog war (also in Ezekiel 38 and 39), after which, there will be at least 7 years of history (Ezekiel 39:9), and, at some time beyond that, the appearing of Christ, wherein, the sun will be darkened and the moon will not give her light.
At this, then, apparently will be the sounding of the last trumpet, with the shout of the Archangel, and the elements will be destroyed in fervent heat.