Not 3–1/2 or 7 years 

Only three verses in the Bible use the phrase "great tribulation" and none refers to a yet-future 3–1/2 or 7 year time of severe trial...

For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be. (Matthew 24:21)

From the context we see that this refers to the destruction of Jerusalem and the temple in 70 A.D.

Behold, I will cast her into a bed, and them that commit adultery with her into great tribulation, except they repent of their deeds. (Revelation 2:22)

This verse has nothing to do with "the Great Tribulation". It refers to a person or Church in 96 A.D.

And I said unto him, Sir, thou knowest. And he said to me, These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb. (Revelation 7:14)

This verse refers to Christian martyrs throughout the centuries. It's called "great tribulation" because Christians were persecuted and even martyred for their faith.

Many Christians are taught there will be a yet-future 3–1/2 or 7 year "great tribulation" before the second coming of Christ but the passages used to support this are better interpreted to refer to persecution and trouble for believers: (1) in general during the entire church age, and (2) in particular during the first few centuries of the church by the Roman Empire.

Wrath is not the Great Tribulation

Elsewhere I illustrate the meanings of the word "wrath". The following shows it doesn't mean "great tribulation".

Do not take revenge, my friends, but leave room for God's wrath, for it is written: "It is mine to avenge; I will repay," says the Lord. (Romans 12:19)

This does not refer to the great tribulation.

For God did not appoint us to suffer wrath but to receive salvation through our Lord Jesus Christ. (1 Thessalonians 5:9)

The wrath is not a yet-future great tribulation. Here's why: Paul is writing to the church in Thessalonica in 51 A.D. and tells them they will not suffer this wrath. Why would a great tribulation 2,000–plus years in the future matter to them? I doubt Paul consoled people with false promises.

In this way they always heap up their sins to the limit. The wrath of God has come upon them at last. (1 Thessalonians 2:16)

This verse proves the word "wrath" isn't a yet-future great tribulation. Here's why: Paul tells them the wrath of God has finally come upon the ungodly Jews who killed Jesus and persecuted the true church. But these would have died 2,000–plus years too soon.

Note that the "wrath" is a result of their "heaping up their sins to the limit" which is an ongoing occurrence. Paul is merely saying God will even judge the sins of Jews. They are not exempt from judgment based on national identity but must receive salvation the same way as everybody else — through faith in Christ.

Because of these, the wrath of God is coming. (Colossians 3:6)

Paul is referring to sinful activities resulting in the coming of God's wrath. Why would God destroy the world for 3–1/2 or 7 years in a yet-future global great tribulation for the sins of unbelievers living at the time the book of Colossians was written?

Whoever believes in the Son has eternal life, but whoever rejects the Son will not see life, for God's wrath remains on him. (John 3:36)

God's wrath is upon everyone and is only removed through faith in Christ. Therefore, the word "wrath" does not refer to the great tribulation since this event will not affect all unbelievers. Rather, the word "wrath" refers to final judgment.

But because of your stubbornness and your unrepentant heart, you are storing up wrath against yourself for the day of God's wrath, when his righteous judgment will be revealed. (Romans 2:5)

Does the phrase "day of God's wrath" refer to the great tribulation? Why no; here's why. Paul is referring to unbelievers, to all unbelievers, not just those who will live during a yet-future great tribulation. Therefore the word "wrath" refers to judgment against all unbelievers. This is, of course, final judgment.

The "day of the Lord" is merely the "day" in which God pours out his "wrath".

A third angel followed them and said in a loud voice: "If anyone worships the beast and his image and receives his mark on the forehead or on the hand, he, too, will drink of the wine of God's fury, which has been poured full strength into the cup of his wrath. He will be tormented with burning sulfur in the presence of the holy angels and of the Lamb". (Revelation 14:9-10)

It is significant that God only pours out his wrath on those who worship the beast and who receive the mark. Therefore, the word "wrath" doesn't refer to the great tribulation since at that event there would be believers present.

Kiss the Son, lest he be angry and you be destroyed in your way, for his wrath can flare up in a moment. Blessed are all who take refuge in him. (Psalms 2:12)

The word "wrath" does not refer to the great tribulation, nor does it refer to the millennial rule of Christ (ala premillennialism). The warning is to remind us that God hates sin and will judge sin. We should never trust in God's patience as an excuse to sin because his hatred of sin "can flare up in a moment".

Therefore wait for me," declares the LORD, "for the day I will stand up to testify. I have decided to assemble the nations, to gather the kingdoms and to pour out my wrath on them — all my fierce anger. The whole world will be consumed by the fire of my jealous anger. (Zephaniah 3:8)

This verse clearly doesn't refer to a yet-future great tribulation. In the great tribulation God doesn't assemble all the nations nor does he gather the kingdoms until the very end — instead, God pours out judgment upon the whole world.