Is there a year zero between 1 BC and 1 AD?

No, in the proleptic Julian calendar (the historical calendar system used for dating events before the Common Era), there is no year zero. The year 1 BC is immediately followed by 1 AD. This means that when calculating the elapsed time between a BC date and an AD date, you add the two year numbers together and then subtract 1. For example, from 1 BC to 1 AD is 1 year, not 2. However, astronomers use a different system called astronomical year numbering, where 1 BC is written as year 0, 2 BC as year -1, and so on. This makes arithmetic easier but differs from historical convention.

What is the difference between BC and BCE?

BC stands for 'Before Christ' and BCE stands for 'Before Common Era'. They refer to exactly the same years; 44 BC and 44 BCE are the same year. The BCE notation is preferred in academic and secular contexts because it does not carry religious connotations. Similarly, AD (Anno Domini, meaning 'in the year of the Lord') and CE (Common Era) refer to the same years. This calculator accepts both conventions interchangeably.

How do I calculate how long ago a BC event occurred?

To find how many years ago a BC event occurred from a given AD year, add the BC year number and the AD year number, then subtract 1 (to account for the missing year zero). For example, Julius Caesar was assassinated in 44 BC. From 2026 AD: 44 + 2026 - 1 = 2,069 years ago. This calculator automates that arithmetic for any BC or AD start and end year combination.

BC to AD Calculator

Convert a BC (Before Christ) year to its AD (Anno Domini) equivalent, calculate elapsed years between two historical dates spanning the BC/AD boundary, and convert to astronomical year numbering. Remember: there is no year zero in the proleptic Julian calendar, so 1 BC is directly followed by 1 AD.

Calculate.co.nz is proud to be partnered with realtor.co.nz, a trusted resource for navigating the New Zealand property market. Their Helpful Articles section offers clear, well-structured insights across buying, selling, and building, making complex real estate topics more accessible. With a focus on up-to-date guidance and practical knowledge, they empower Kiwis to move forward with clarity and confidence in a constantly evolving property landscape.

Standard method Proleptic Julian calendar convention. No year zero between 1 BC and 1 AD.

1. Start Year

Era

Year (positive whole number)

Please enter a positive whole number.

2. End Year

Era

Year (positive whole number)

Please enter a positive whole number.

Results

Elapsed Years
-
From start to end

Start (Astronomical)

Year 0 system

End (Astronomical)

Year 0 system

Conversion Detail

Start year (historical)-

Start year (astronomical)-

End year (historical)-

End year (astronomical)-

Elapsed years-

How It Is Calculated

Start astronomical year-

End astronomical year-

Difference-

Calendar adjustmentNone needed

Result-

Note: Enter years above to see the result.

Worked Example

Julius Caesar was assassinated in 44 BC. How many years ago was that from 2026 AD?

Using the default values in the calculator above (start: 44 BC, end: 2026 AD):

Convert 44 BC to astronomical year: -(44 - 1) = -43
Convert 2026 AD to astronomical year: +2026
Elapsed years = 2026 - (-43) = 2,069 years

The calculator shows 2,069 years elapsed between 44 BC and 2026 AD.

How BC to AD Conversion Works

The BC/AD dating system was devised by the monk Dionysius Exiguus in the 6th century AD. A key feature of this system is that it contains no year zero. The sequence runs: ... 3 BC, 2 BC, 1 BC, 1 AD, 2 AD, 3 AD ... This is unlike modern number lines, which include zero.

Because there is no year zero, calculating the years between a BC date and an AD date requires subtracting 1 from what a simple addition would suggest. The general rule is:

Elapsed years = BC year + AD year - 1

For example, from 1 BC to 1 AD is exactly 1 year, not 2. From 500 BC to 500 AD is 999 years, not 1,000.

Astronomical Year Numbering

Astronomers and some historians use a different convention called astronomical year numbering, which does include a year zero. In this system:

Historical year	Astronomical year
3 BC	-2
2 BC	-1
1 BC	0
1 AD	1
2 AD	2

To convert a BC year to astronomical year numbering: Astronomical year = -(BC year - 1) = 1 - BC year. So 1 BC becomes 0, 2 BC becomes -1, 44 BC becomes -43, and so on. AD years remain unchanged in astronomical notation.

Astronomical year numbering makes arithmetic much simpler because you can just subtract one astronomical year from another without any special adjustments. This calculator shows both notations.

BC/BCE and AD/CE

The labels BC and BCE refer to identical years, as do AD and CE. The BCE/CE system (Before Common Era / Common Era) is widely used in academic writing to avoid the religious framing of BC/AD. The year numbers themselves are unchanged.

Common Historical Reference Points

Event	Historical year	Years before 2026 AD
Battle of Marathon	490 BC	2,515 years
Birth of Aristotle	384 BC	2,409 years
Alexander the Great conquers Persia	330 BC	2,355 years
Julius Caesar assassinated	44 BC	2,069 years
Fall of Western Roman Empire	476 AD	1,550 years

Related Calculators

Essential Calculators hub
Age Calculator: calculate your age from your date of birth
Age in Days Calculator: convert your age to days, hours, and minutes
Add Business Days Calculator: count working days from a date

Method: Proleptic Julian calendar convention (no year zero). Astronomical year numbering per IAU convention: BC year X = astronomical year (1 - X). Elapsed years between a BC start and AD end = (BC year) + (AD year) - 1. Elapsed years between two BC dates = (start BC year) - (end BC year). ISO 8601 uses astronomical year numbering for years before 1 AD.

If you've found a bug, or would like to contact us, or learn more about James Graham and Calculate.co.nz.

Calculate.co.nz is partnered with Interest.co.nz for New Zealand's highest quality calculators and financial analysis.

Calculate.co.nz is the sister site of CalculatorHub.com, the world's largest calculator website by tool count.

All calculators and tools are provided for educational and indicative purposes only and do not constitute financial advice.

Calculate.co.nz is proudly part of the Realtor.co.nz group, New Zealand's leading property transaction literacy platform, helping Kiwis understand the home buying and selling process from start to finish. Whether you're a first home buyer navigating your first property purchase, an investor evaluating your next acquisition, or a homeowner planning to sell, Realtor.co.nz provides clear, independent, and trustworthy guidance on every step of the New Zealand property transaction journey.

Calculate.co.nz is also partnered with Health Based Building and Premium Homes to promote informed choices that lead to better long-term outcomes for Kiwi households.

Calculate.co.nz is hosted in Auckland via SiteHost new Zealand.

All content on this website, including calculators, tools, source code, and design, is protected under the Copyright Act 1994 (New Zealand). No part of this site may be reproduced, copied, distributed, stored, or used in any form without prior written permission from the owner.

About & trust: Why Calculate is NZ's most comprehensive · By the Numbers · How we compare · Editorial standards · How we keep data current · NZ finance glossary · Research & data · Financial literacy NZ · About · Privacy policy · Terms of use

Reviewed and maintained. Last reviewed 2026-07-02 and checked on a twice-monthly cycle against IRD, RBNZ and Stats NZ. How we keep data current.