How to Use Timestamp Converter
Follow these three steps to process, validate, and export your data locally inside your browser with zero server latency:
Enter a Unix timestamp (auto-detected as seconds or milliseconds, or selectable manually) or pick a calendar date/time.
Inspect the corresponding ISO 8601 string, UTC string, local timezone representation, and relative time.
Copy any representation with one click.
Understanding Unix Epoch Time, Millisecond Precision & ISO 8601 UTC Serialization
Unix time (also known as POSIX time or Epoch time) represents a point in time as a single monotonically increasing integer: the number of elapsed seconds (or milliseconds) since 00:00:00 UTC on January 1, 1970, excluding leap seconds. Because a Unix timestamp is completely independent of local time zones and Daylight Saving Time rules, it is the universal standard for JWT expiration claims (exp, iat), database audit logs, and distributed event streams.
A common friction point when debugging APIs is mixing 10-digit Unix seconds (used by Python time.time(), Go, PHP, and JWT claims) with 13-digit Unix milliseconds (used by JavaScript Date.now() and Java System.currentTimeMillis()). Our Timestamp Converter automatically detects whether your input is in seconds or milliseconds and outputs synchronized Seconds, Milliseconds, ISO 8601 UTC, RFC/UTC String, Local Time, and Relative Time.
The Year 2038 Problem (Y2K38) Explained
Legacy systems that store Unix timestamps in a signed 32-bit integer will overflow after 2,147,483,647 seconds on January 19, 2038 at 03:14:07 UTC, wrapping around to December 13, 1901. Always use 64-bit integers (BIGINT in SQL) or ISO 8601 strings for dates extending beyond 2038.
Unix Timestamp Precision Across Programming Languages
Quick lookup for how major languages and standards generate current epoch timestamps:
| Language / Standard | Native Expression | Default Unit | Example Value |
|---|---|---|---|
| JavaScript / TypeScript | Date.now() | Milliseconds (13 digits) | 1735689600000 |
| JSON Web Token (JWT exp/iat) | NumericDate (RFC 7519) | Seconds (10 digits) | 1735689600 |
| Python 3 | int(time.time()) | Seconds (10 digits) | 1735689600 |
| PostgreSQL | EXTRACT(EPOCH FROM NOW()) | Seconds (with fractional) | 1735689600.123 |
| Go (Golang) | time.Now().Unix() / .UnixMilli() | Seconds or Milliseconds | 1735689600 |
Timestamp Debugging & Time-Zone Best Practices
Eliminate off-by-1000x bugs and time-zone confusion in distributed systems:
1. Inspecting JWT exp and iat Claims
Auth DebuggingPaste the 10-digit exp number from a decoded JWT payload to see the exact UTC and local expiration time plus a relative "in X hours / X days ago" readout.
2. Bidirectional ISO 8601 & Date String Parsing
Reverse LookupSwitch to the "ISO / Date String -> Timestamp" tab and enter any ISO 8601 date (e.g., 2026-06-15T14:30:00Z) to get its exact 10-digit and 13-digit epoch values.
3. Always Store & Transmit Timestamps in UTC
Backend ArchitectureStore timestamps as UTC in your database and convert to the user’s local time zone only at the presentation layer in the browser.
4. One-Click "Use Current Time (Now)" Sync
Quick TestingClick "Use Current Time (Now)" to populate the current millisecond epoch for generating fresh test payloads or cache-busting parameters.
Practical Examples & Input/Output Reference
Converting a Unix epoch second value to UTC
Inspecting timestamp `1700000000`.
Sample Input
1700000000 (Seconds)Expected Output
ISO 8601: 2023-11-14T22:13:20.000Z | Milliseconds: 1700000000000Frequently Asked Questions
How does the tool distinguish between seconds and milliseconds?
In auto-detect mode, timestamps with 12 or more digits (or absolute values ≥ `100,000,000,000`) are treated as milliseconds, while 10-digit values are treated as seconds. You can also explicitly override the unit.