Question 1

Coordinated Universal Time (UTC)

Accepted Answer

is the primary time standard by which the world regulates clocks and time. It is not a time zone, but rather the foundational standard from which all time zones are calculated. Timestamps are inherently tied to UTC. A Unix timestamp of 1600000000 represents the exact same moment in time regardless of where you are on Earth. Timezone Offset is the positive or negative difference in hours and minutes between UTC and a specific local time. For example, Eastern Standard Time (EST) has an offset of UTC-5, meaning it is exactly five hours behind Coordinated Universal Time.

Question 2

What happens if a timestamp is a negative number?

Accepted Answer

A negative timestamp simply represents a date and time prior to the Unix epoch of January 1, 1970, 00:00:00 UTC. For example, a timestamp of -86400 (exactly one day of seconds) represents December 31, 1969, at 00:00:00 UTC. The mathematical conversion works exactly the same way, simply counting backward from the epoch. Modern 64-bit systems can handle negative timestamps effortlessly, allowing them to represent dates billions of years in the past.

Question 3

How do leap seconds affect timestamps?

Accepted Answer

Standard Unix timestamps completely ignore leap seconds. When an international leap second is added (e.g., 23:59:60), the Unix clock simply repeats the integer from the previous second, or slightly slows down its tick rate to "smear" the extra second over a 24-hour period (a technique used by Google). Therefore, you cannot simply subtract two timestamps to find the exact number of atomic seconds between two events if a leap second occurred between them.

Question 4

Why do some timestamps have 13 digits instead of 10?

Accepted Answer

A 10-digit timestamp represents the number of seconds since the epoch. A 13-digit timestamp represents the number of milliseconds (thousandths of a second) since the epoch. Programming environments like JavaScript natively generate 13-digit timestamps to provide higher precision for performance tracking and UI events. To convert a 13-digit timestamp to a standard 10-digit timestamp, simply divide it by 1,000 and drop the decimal.

Question 5

Is Unix time the same on Windows and Mac?

Accepted Answer

Yes, the concept of standard Unix time (seconds since Jan 1, 1970) is universally respected across modern Windows, macOS, and Linux systems for internet communications and standard programming APIs. However, deep within their proprietary file systems, they may use different epochs. NTFS (Windows) uses Jan 1, 1601, and Core Data (Apple) uses Jan 1, 2001. When working with high-level web development, you will almost exclusively encounter the 1970 standard.

Question 6

How do I handle historical dates before 1970?

Accepted Answer

If you are using a modern system with 64-bit integers, you handle them exactly the same way as post-1970 dates; the system will simply generate a negative integer. However, if you are working with legacy 32-bit systems, or if your dates pre-date the Gregorian calendar shift (1582), integer timestamps become unreliable. For deep historical dates, best practice is to store the year, month, and day as separate columns in your database or use formatted ISO 8601 strings.

Question 7

What is the maximum date a 64-bit timestamp can hold?

Accepted Answer

A 64-bit signed integer can hold a maximum value of 9,223,372,036,854,775,807. If we treat this as seconds since 1970, it translates to a date approximately 292 billion years in the future (specifically, Sunday, December 4, 292,277,026,596 AD). This is roughly 21 times the current estimated age of the universe. Therefore, a 64-bit timestamp effectively solves the integer overflow problem permanently for all practical human applications.

Timestamp to Date Converter

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