BC and AD on a timeline
BC years count down, AD years count up, and there is no year 0 in between. That one missing year trips up timelines, homework and date calculators alike. Here's how the system works, and a line you can drag to see it.
The missing year zero
When Dionysius Exiguus set up the Anno Domini count in AD 525, European mathematics had no zero. So the count simply starts at 1: the year before AD 1 is 1 BC.
That means you can't treat BC years as negative numbers and subtract. From 1 BC to AD 1 is one year, not two. Crossing the divide, add the two years and subtract one.
Drag the markers on the number line to feel it: every cell is a year, and the shaded cells are the years that actually pass. There is simply no cell labelled 0.
Astronomers sidestep the problem by numbering 1 BC as year 0 and 2 BC as −1. TimelineForge uses that arithmetic internally to place events, then shows you the historian's labels.
From 4 BCE to 6 CE is
9 years
Plain subtraction (6 + 4) gives 10 — one too many, because the count jumps from 1 BCE straight to 1 CE.
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← BCECE →
Drag the numbered markers, or focus one and use the arrow keys. Each cell is a whole year; the shaded cells are the years that actually elapse.
Years between two dates
Type any two years in BC/BCE or AD/CE form.
2,069 years from 44 BCE to 2026 CE (no year 0 counted)
Centuries across the divide
| Century | Runs from | To |
|---|---|---|
| 5th century BCE | 500 BCE | 401 BCE |
| 1st century BCE | 100 BCE | 1 BCE |
| 1st century CE | 1 CE | 100 CE |
| 2nd century CE | 101 CE | 200 CE |
| 20th century CE | 1901 CE | 2000 CE |
| 21st century CE | 2001 CE | 2100 CE |
Centuries start in a year ending in 1, which is why the 21st century began on 1 January 2001, not 2000.
Before anyone numbered years, people counted months by the Moon — "month" and "moon" share an Old English root. ahaboo has a narrated explainer on why its phases change.
BC/AD or BCE/CE: which should your timeline use?
The numbers are identical, so choose by audience. Many schools, museums and academic publishers use BCE/CE; many popular books and older curricula use BC/AD. Whichever you pick, be consistent across the whole timeline.
- Write AD before the year (AD 79) and BC after (44 BC). BCE and CE both follow the year.
- You only need to label AD/CE years when the timeline also contains BC/BCE years, or when the dates are early enough to be ambiguous.
- For approximate dates, write c. (circa): c. 2560 BCE.
The history timeline maker handles all of this for you: type dates any way you like, toggle BCE/CE or BC/AD, and the axis skips year zero correctly. Try it on the Ancient Rome or Ancient Egypt templates.
BC, AD, BCE and CE questions
What do BC and AD mean?
BC stands for "Before Christ" and AD for "Anno Domini", Latin for "in the year of the Lord". The system was devised by the monk Dionysius Exiguus in AD 525 and popularised by Bede in the 8th century.
What do BCE and CE mean?
BCE means "Before Common Era" and CE means "Common Era". They number years exactly the same way as BC and AD — 500 BCE is 500 BC and 2026 CE is AD 2026 — but avoid a religious reference. BCE/CE is standard in many academic and museum contexts.
Is there a year 0?
No. In the BC/AD and BCE/CE systems, 1 BC is followed directly by AD 1. Astronomers use a different numbering that does include a year 0 (astronomical year 0 equals 1 BC), which is why calculators sometimes disagree by one.
How do you count years from BC to AD?
Add the two numbers and subtract one. From 44 BC to AD 2026 is 44 + 2026 − 1 = 2069 years. If both dates are BC, or both are AD, just subtract the smaller from the larger.
Why do BC years count down?
BC years are counted backwards from the start of the AD era, so bigger numbers are further in the past. 500 BC came before 400 BC, and the "5th century BC" runs from 500 BC down to 401 BC.
Does AD go before or after the number?
Traditionally AD goes before the year (AD 79) and BC after it (44 BC). BCE and CE both go after the year (44 BCE, 79 CE). TimelineForge follows these conventions when you switch label styles.