Some will say that the ‘Old Testament’ prophet was more predictive, or that New Testament Prophet is really just in place to confirm things God has already told you. However, the NT prophet isn’t always just in place to confirm. I’ve often told people things they had no clue were going to happen, usually with them insisting I was wrong until it came to pass. John, the writer of Revelation, wrote a whole book of predicting prophecies. The prophecy of Agabus in Acts 21 wasn’t a confirmation to the disciples; the narrative makes it clear that they didn’t know until then that Paul was headed for more trouble than usual at Jerusalem.

The nature of prophecy has not really changed from the OT to the NT. The indwelling of the Holy Spirit doesn’t change the source of genuine prophecy. The only real change has been that with the Holy Spirit being given to people, it is now possible for people to have a gift of prophecy without being a prophet. The fact that God has spoken or otherwise revealed something remains. However, a great many teachers on the subject tried to create a distinction between the two outside of this detail in order to justify errors and inconsistencies.
One thing I’ve learned about predictive over the years is that unless the prophecy has some definite conditions attached to it, faith isn’t necessary for it to come to pass. If God said it will happen, it will happen. I’ll share an example:

In 2010, my wife and I were gong to spend the summer in New Brunswick. I had felt that a major natural disaster was coming, and so my wife was worried. The Lord said to me, ‘For you, I will stay my hand.’ I told my wife I thought it wouldn’t happen until we left, but I didn’t really believe it was going to happen. The very day we left, precisely at the moment we crossed into Quebec as we left New Brunswick, a storm began that turned out to be the greatest Natural Disaster in New Brunswick’s history. Though I hadn’t really believed it, it came to pass. Usually when a ‘prophet’ tries to pin a prophetic failure on a lack of faith or obedience, it’s a cop-out. Though we are in the NT, Romans 8 tells us that the work of Christ and the Holy Spirit are to establish the righteousness of the Law in us… and we are elsewhere told that the OT is the shadow of the NT… so the principles of prophecy never changed… ‘… if the thing follow not, nor come to pass, then that is the thing which the Lord has not spoken…’ (Deut. 18:22).
Now, we further must understand that the portion of the Bible which we commonly call the ‘Old Testament’ is more than just the Old Testament. The Testament consists of the Law, which is only a portion of those books. This is why Jesus made the distinction of ‘The Law and the Prophets.’ Deuteronomy 18:15-22 would not constitute Law, but rather would be part of the prophetical writings, since it contains both a messianic prophecy AND a paradigm for the character and conduct of a prophet contained within that prophecy which clearly pointed to the NEW testament, since it is messianic…
This has tremendous implications for accountability, and my challenge to you is to examine your own life and ministry, and pursue a closer walk with God.