Seconds/Days Since Year 0 Calculator

Enter a date (year, month, day) and instantly see how many seconds and days have elapsed since Year 0 (0000-01-01). Results also include seconds since 1 AD, days since 1 AD, days since 1900, days since 1904, and days since the Unix epoch (1970) — all in one place.

Results

Seconds Since Year 0

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Days Since Year 0

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Seconds Since 1 AD (0001-01-01)

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Days Since 1 AD (0001-01-01)

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Days Since 1900-01-01

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Days Since 1904-01-01

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Days Since Unix Epoch (1970-01-01)

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Seconds Since Unix Epoch (1970-01-01)

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Frequently Asked Questions

What is Year 0 in this calculator?

Year 0 is defined as 0000-01-01 00:00:00 UTC, which is a proleptic Gregorian calendar concept. It is not a historically valid date — there was no Year 0 in the standard historical calendar — but it is used as a reference point by systems like MySQL's TO_SECONDS() function.

How is 'Seconds Since Year 0' calculated?

The calculator counts the total number of seconds from 0000-01-01 00:00:00 UTC to your entered date and time. It accounts for leap years using the proleptic Gregorian calendar rules, giving the same result as MySQL's TO_SECONDS() function.

What is the difference between Year 0 and 1 AD as a reference point?

Year 0 (0000-01-01) is one year earlier than 1 AD (0001-01-01). Therefore, 'Seconds Since Year 0' is always larger than 'Seconds Since 1 AD' by exactly 31,622,400 seconds (366 days × 86,400, since year 0 is a leap year).

Why do Excel and spreadsheets use days since 1900 or 1904?

Microsoft Excel's date serial numbers are based on days since January 1, 1900, with a deliberate off-by-one bug that treats 1900 as a leap year. Older Macintosh versions of Excel used January 1, 1904, as their base date instead. This calculator shows both for compatibility purposes.

What is the Unix epoch and why is it important?

The Unix epoch is January 1, 1970, 00:00:00 UTC. It is the standard reference point for Unix timestamps used in most programming languages, databases, and operating systems. The number of seconds since the Unix epoch is often called a 'Unix timestamp' or 'POSIX time'.

Does this calculator account for leap years?

Yes. The calculation uses the proleptic Gregorian calendar rules: a year is a leap year if it is divisible by 4, except for century years, which must be divisible by 400. This means 2000 is a leap year but 1900 is not.

What happens if I enter a date before 1970?

For dates before January 1, 1970, the 'Days Since Unix Epoch' and 'Seconds Since Unix Epoch' outputs will display as negative numbers, which is the correct mathematical result — those dates preceded the Unix epoch.

Can I use this to find the MySQL TO_SECONDS() value for a date?

Yes. MySQL's TO_SECONDS() function counts seconds from 0000-00-00 00:00:00. This calculator's 'Seconds Since Year 0' output is compatible with that function, making it useful for database work and MySQL date arithmetic.

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