Calculation in AD (Anno Domini)
A monk in the sixth century in (from) northern Europe calculated that Jesus of Nazareth was born 754 years after the City of Rome was built (founded) and he took this year as the first year of AD and this has been used ever since.

This calculation was wrong! According to the information obtained from later research, Jesus was actually born between 7-5 BC.

Neither was Jesus born on the 25th of December. The date and month of Jesus’ birth are not known. Christians celebrate Christmas on December 25th each year, which is just a tradition derived from believers in the fourth century. They took the day when the Romans celebrated the sun god to celebrate the birthday of Jesus who was the sun of righteousness in their heart.

The date of Jesus' death can be determined, but the year is unknown. Jesus was nailed to the cross on the Jewish Passover preparation day , the day before the Sabbath. Based on the data of Passover and Sabbath, it is very likely that Jesus died in 30 or 33 AD. Most of the current biblical scholars believe that 30 AD is more accurate. Jesus died at the age between 35 and 38 years old.