Calculating Time BC and AD The Current System . The calendar and dating system we use today is called the Gregorian Calendar . it was adopted by Pope Gregory XIII in the mid-1500s . it is based on the life of Jesus Christ Before Christ (BC) . years followed by BC indicate that a certain event happened before the birth of Jesus Christ . for example: 150 BC indicates 150 years before the birth of Jesus Christ Anno Domini (AD) . years followed by AD indicate that a certain event happened after the birth of Jesus Christ . AD is Latin for “In the year of the Lord” . for example: the current year, 2012 AD, indicates that this is the 2,012th year since the birth of Jesus Before the Common Era (BCE) . In many cases, you will see the abbreviation BCE used instead of BC - WHY? . The Gregorian Calendar is a Christian calendar, so some non- Christians use BCE as an alternative (politically correct) Common Era (CE) . in many cases, you will see the abbreviation CE used instead of AD . WHY? . Again, this is a non-Christian alternative Timeline BC (BCE) AD (CE) 9 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 9 Calculating Time . When both dates are AD, just subtract the years how long between 10 AD and 140 AD? 130 years (140 -10) Calculating Time . When both dates are BC, just subtract the years how long between 5 BC and 500 BC? 495 years (500-5) Calculating Time . When one date is AD, and one is BC, add the two years } after that, subtract one . how long between 5 BC and 10 AD? . 14 years ([5 + 10] -1) . why subtract 1? (no year 0) Calculate . How long between 2004 AD and 1950 AD? 54 years . How long between 1234 AD and 1492 AD? 258 years Calculate . How long between 54 BC and 230 BC? 176 years . How long between 2500 BC and 1200 BC? 1300 years Calculate . How long between 2004 BC and 2004 AD? 4,007 years . How long between 540 AD and 100 BC? 639 years .