Epoch Converter

An epoch converter translates a numeric timestamp into a human-readable date and time — and vice versa — across multiple epoch systems used by different operating systems, programming languages, and network protocols. An epoch is simply a fixed reference point in time from which timestamps are counted, usually in seconds, milliseconds, or smaller units.

Different computing platforms chose different epochs for practical and historical reasons. Unix systems count seconds from January 1, 1970; Windows uses January 1, 1601 (the start of a Gregorian 400-year cycle); GPS satellites count from January 6, 1980; and NTP network time uses January 1, 1900. Converting between these systems is a frequent task for developers, system administrators, and data engineers.

This epoch converter supports six major epoch systems — Unix, Windows FILETIME, Apple Cocoa, GPS, NTP, and Julian Date — and accepts input in seconds, milliseconds, microseconds, or nanoseconds. The result includes both the human-readable date and the equivalent numeric values across all supported epoch systems.

All epoch conversions share the same underlying mathematics: subtract (or add) the difference between two epochs' reference points to translate a timestamp from one system to another.

Each computing domain selected an epoch that made sense for its era and purpose:

Timestamps can be expressed at different resolutions depending on the application's precision needs:

• Seconds: The classic Unix timestamp format. Example: 1717718400 = June 7, 2024 00:00:00 UTC. Used in most web APIs and log files.
• Milliseconds: Standard in JavaScript (Date.now() returns milliseconds). Multiply the seconds value by 1,000. Example: 1717718400000.
• Microseconds: Multiply the seconds value by 1,000,000. Used in high-resolution system clocks and databases like PostgreSQL.
• Nanoseconds: Multiply the seconds value by 1,000,000,000. Used in Go's time package and precision hardware timestamping.

This converter accepts all four formats and normalizes them to milliseconds internally before performing epoch comparisons.

Epoch conversion is a daily task in software engineering and data analysis. When debugging API responses, developers often encounter Unix timestamps that need to be converted to readable dates. Log analysis tools display events in epoch time, and converting them is essential for correlating incidents across systems.

Database engineers working with Windows systems frequently encounter FILETIME values stored in NTFS metadata, Active Directory attributes, and Exchange email headers. Converting these to Unix time or ISO dates is necessary for cross-platform data pipelines.

GPS and telecommunications engineers deal with GPS epoch time when processing satellite data, navigation fixes, and GNSS (Global Navigation Satellite System) signals. GPS time does not include leap seconds, which creates an additional offset from UTC that grows over time.