Seconds/Days Since Year 0 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.

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.

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).

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.

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'.

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.

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.

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.