BC to AD Calculator by Omni

How to Calculate BC Years?

Calculating BC (Before Christ) years can be confusing at first, BC years count backwards from the year 1 BC, which is immediately followed by 1 AD (Anno Domini).

To calculate BC years, you need to:

1. Identify the reference point (usually 1 BC/AD)
2. Count backwards from that point
3. Remember that there is no year zero

Let’s calculate how many years passed between 753 BC (the traditional founding of Rome) and 44 BC (the assassination of Julius Caesar):

Start with 753 BC

Count backwards to 44 BC

753 – 44 = 709 years

When calculating across the BC/AD boundary, you need to subtract one year to account for the lack of a year zero. For instance, to calculate the years between 100 BC and 100 AD:

1. 100 years BC + 100 years AD = 200 years
2. Subtract 1 year (no year zero)
3. Final result: 199 years

BC to AD Conversion Chart

BC to AD Conversion Formula

The formula for converting BC years to AD years is:

AD year = (BC year × -1) + 1

This formula works because it:

1. Reverses the BC year (multiplying by -1)
2. Adjusts for the lack of a year zero (adding 1)

Examples:

Convert 753 BC to AD: AD year = (753 × -1) + 1 = -752 + 1 = -751 AD (This means 753 BC is equivalent to 751 AD in the opposite direction)

Convert 44 BC to AD: AD year = (44 × -1) + 1 = -43 + 1 = -42 AD

Remember that negative AD years are equivalent to BC years, so -42 AD is the same as 42 BC.

1 BC is Equal To How Many Years

1 BC is equal to 1 year before the start of the AD era. 1 BC is immediately followed by 1 AD, with no year zero in between.

This can be visualized as a number line where 1 BC is -1, and 1 AD is 1, with 0 omitted.

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