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
th
AD, indicates that this is the 2,012
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 nonChristians 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