It has been exceedingly difficult to harmonise the gospel of John with Matthew, Mark and Luke during the time of Jesus’ early ministry. This is because the synoptic gospels miss out the time from his temptation unto his Galilean ministry. They jump straight from in the wilderness in Judea to Galilee. John, on the other hand, details several months between in Judea and Samaria.
Here is a diagram that is easy to follow. I hope it helps anyone who might have problems with so-called contradictions in the New Testament.