Most likely, Jesus was born around 4-6BCE.

There is no year 0. It goes from 1 BCE to 1 CE

We can be certain Jesus was born around 4-6 BCE based on clues in the birth narratives. While much of the birth narratives are mythological, there are also portions that are most likely history remembered. The date is also supported by the Gospel of John.

Some key points is that he is said to have been born around the time of the death of King Herod. Hes also said to be around 30 when he started preaching, which was the 15th year of the reign of Tiberius Caesar.

This puts the date right around 4-6 BCE.

I was homeschooled in a home that had a homemade timeline on the wall of our "class room" that looked vaguely like this:

<----1 BC [crucifix] AD 1---->

if that makes any sense. I mention this because I understand your question. The spacial separation of BC and AD on the timeline in my home made it look like there should be a temporal separation as well. Unfortunately that was misleading. There is no 0 year on the BC/AD scale. It goes from 1 BC to AD 1.

In addition to the 0 year problem, the date of the birth of Christ is debated. The question revolves around the governorship of Quirinius in Syria and the reign of Herod. In Luke those are contemporaneous, but we know Herod died in 4 BC, and Quirinius was governor of Syria in AD 6. So we have a 10 year frame for the birth of Christ that people go back and forth on.