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How to calculate years between historical dates

BCE and CE dates meet at year 1 — there is no year 0. Here is how to count the years between events across the eras.

Historians count years in two eras: BCE (Before the Common Era) and CE (Common Era). The key trap: there is no year 0.

Same era

Within one era, subtract the smaller year from the larger.

Between 100 BCE and 300 BCE: 300−100=200300 - 100 = 200 years.

Crossing the eras

When one date is BCE and the other is CE, add the two years.

Between 44 BCE (the death of Julius Caesar) and 476 CE (the fall of the Western Roman Empire): 44+476=52044 + 476 = 520 years.

Why add?

The timeline runs …, 2 BCE, 1 BCE, 1 CE, 2 CE, … so the distance from 1 BCE to 1 CE is exactly 1 year, not 2. Adding accounts for that. Practise with randomised date-math questions below.