Daniel 9:24-26 is where we find it. It says: "Listen, and understand. Seven sevens plus sixty-two sevens will pass from the time the command is given to rebuild Jerusalem until a ruler – the Messiah – comes. Jerusalem will be rebuilt with streets and strong defenses, despite the distressing times. After this period of sixty-two sevens, the Messiah will be killed…"
So let’s do the math on that: first, it says “Seven sevens plus sixty-two sevens” will pass from the time the command is given to rebuild Jerusalem until the Messiah dies. So that’s 49 (7x7) plus 434 (62x7) = 483 years.
Fortunately, it later tells us when to start the countdown. Nehemiah 2:1-6 states that King Artaxerxes of Persia gave the order in his “twentieth year”, which was 445 BC, according to Britannica (sources at end), in "the month of Nisan" (the Hebrew month corresponding to our March and April).
So, knowing this, we can calculate exactly when it’s saying the Messiah would die. From the command being given to rebuild Jerusalem to the death of the Messiah is 483 years. 483 years after 445 BC would get us 38 AD, but we need to convert the date, as the calendar Daniel was using was slightly different from ours.
Our calendar has 365.25 days, while the Babylonian one Daniel was using had 360 days.
Close enough for now...:)