How long will the Antichrist reign?
Scripture teaches that the Antichrist will be given authority to continue for forty two months, which is three and a half years, described also as a time, times, and the dividing of time.
The Bible gives a clear time frame for how long the Antichrist will be allowed to exercise his full power. Daniel 7:25 says of him that he shall speak great words against the Most High and wear out the saints, and they shall be given into his hand until a time and times and the dividing of time. Daniel 12:7 confirms this same length, stating it shall be for a time, times, and an half, when he shall have accomplished to scatter the power of the holy people.
Revelation makes this period explicit in days and months. Revelation 13:5 says power was given unto the beast to continue forty and two months, which is three and a half years. Revelation 12:14 describes the woman, representing Israel, being nourished in the wilderness for a time, and times, and half a time, from the face of the serpent, the same three and a half year span during which the dragon persecutes her.
This three and a half year reign of terror comes in the second half of a seven year covenant the Antichrist makes with Israel. Daniel 9:27 explains that he shall confirm the covenant with many for one week (seven years), and in the midst of the week he shall cause the sacrifice and the oblation to cease. For the first three and a half years he acts as a deliverer, allowing Israel to rebuild the temple and resume sacrifices. Then, in the middle of the seven years, he breaks the covenant, enters the temple, and demands worship as God, launching the final three and a half years of great persecution against both Israel and the Church, described in Matthew 24:15-22 as the great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be, days that are shortened for the elect's sake.
Throughout that time he is permitted, by God's own ordering, to make war with the saints and overcome them, as Revelation 13:7 states, and to subdue a portion of Israel as well. Yet his time is fixed and limited to that same three and a half year measure until, as Daniel 8:25 declares, he shall also stand up against the Prince of princes but he shall be broken without hand.
The scriptures
And he shall speak great words against the most High, and shall wear out the saints of the most High, and think to change times and laws: and they shall be given into his hand until a time and times and the dividing of time.
And I heard the man clothed in linen, which was upon the waters of the river, when he held up his right hand and his left hand unto heaven, and sware by him that liveth for ever that it shall be for a time, times, and an half; and when he shall have accomplished to scatter the power of the holy people, all these things shall be finished.
And there was given unto him a mouth speaking great things and blasphemies; and power was given unto him to continue forty and two months.
And to the woman were given two wings of a great eagle, that she might fly into the wilderness, into her place, where she is nourished for a time, and times, and half a time, from the face of the serpent.
And he shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease, and for the overspreading of abominations he shall make it desolate, even until the consummation, and that determined shall be poured upon the desolate.
When ye therefore shall see the abomination of desolation, spoken of by Daniel the prophet, stand in the holy place, (whoso readeth, let him understand:) Then let them which be in Judaea flee into the mountains: Let him which is on the housetop not come down to take any thing out of his house: Neither let him which is in the field return back to take his clothes. And woe unto them that are with child, and to them that give suck in those days! But pray ye that your flight be not in the winter, neither on the sabbath day: For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be. And except those days should be shortened, there should no flesh be saved: but for the elect’s sake those days shall be shortened.
And it was given unto him to make war with the saints, and to overcome them: and power was given him over all kindreds, and tongues, and nations.
And through his policy also he shall cause craft to prosper in his hand; and he shall magnify himself in his heart, and by peace shall destroy many: he shall also stand up against the Prince of princes; but he shall be broken without hand.
From the books
This answer is drawn from these passages in the Mary Banks Faith Library.