Epoch Calculator
Epoch calculator works out Unix timestamp (seconds) and Unix timestamp (milliseconds) from Timestamp, Timestamp unit and Date. The default figures on this page give UTC date and time (RFC 3339) of 2023-11-14T22:13:20Z; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
3 steps
- 1700000000 has magnitude 1.70e+9, which falls in the seconds band, so it is read as 1700000000 seconds since the epoch.
- floor(1700000000 / 86400) = 19675 whole days, remainder 80000 s = 22:13:20.
- Day 19675 after 1970-01-01 is 2023-11-14, a Tuesday.
Its 6 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
4 sources
What the epoch calculator calculates
Converts a Unix timestamp in seconds, milliseconds, microseconds or nanoseconds into a UTC date and time, and converts a date and time back into a timestamp. Unix time counts seconds since 1970-01-01T00:00:00Z with every day exactly 86400 seconds long (POSIX ignores leap seconds), so the conversion is exact integer arithmetic and independent of the reader’s time zone.
How to use this epoch calculator
Enter Timestamp, Timestamp unit, Date and Time of day. Unix timestamp (seconds) updates as you type. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Unix timestamp (seconds), Unix timestamp (milliseconds) and Unix timestamp (microseconds).
The method follows IEEE Std 1003.1-2017 (POSIX.1-2017), Base Definitions §4.16, Seconds Since the Epoch, RFC 3339, Date and Time on the Internet: Timestamps, Howard Hinnant, chrono-Compatible Low-Level Date Algorithms and ECMAScript Language Specification, Date.now and time values.
What you can compare
Change one input at a time to see how it affects Unix timestamp (seconds), Unix timestamp (milliseconds) and Unix timestamp (microseconds). The inputs you can vary are Timestamp, Timestamp unit, Date, Time of day and UTC offset of that date and time.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do I convert an epoch time to CST?
Converts a Unix timestamp in seconds, milliseconds, microseconds or nanoseconds into a UTC date and time, and converts a date and time back into a timestamp. Open “How this is worked out” beside the result to see each step for your own figures.
Why was 1970 an epoch?
Converts a Unix timestamp in seconds, milliseconds, microseconds or nanoseconds into a UTC date and time, and converts a date and time back into a timestamp. On the figures this page opens with — timestamp 1,000,000,000 — the UTC date and time (RFC 3339) is 2023-11-14T22:13:20Z. Put your own figures in their place and the working updates beside the result.
What is today's epoch?
Converts a Unix timestamp in seconds, milliseconds, microseconds or nanoseconds into a UTC date and time, and converts a date and time back into a timestamp. On this page it is computed from Timestamp, Timestamp unit and Date and shown as Unix timestamp (seconds), Unix timestamp (milliseconds) and Unix timestamp (microseconds).
How do I convert an epoch to a human-readable date?
It needs Timestamp, Timestamp unit, Date, Time of day and UTC offset of that date and time. Nothing else is required, and the figures stay in your browser.
What information do I need for the epoch calculator?
You need Timestamp, Timestamp unit, Date, Time of day and UTC offset of that date and time. The page opens with default figures that give UTC date and time (RFC 3339) of 2023-11-14T22:13:20Z, so you can see the scale before entering your own.
What does this epoch calculator show?
It shows Unix timestamp (seconds), Unix timestamp (milliseconds), Unix timestamp (microseconds), UTC date and time (RFC 3339), UTC date, UTC time, Weekday (UTC) and Day of the year (UTC), with the working and any warnings for your entries.