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Unix Timestamp Converter Guide — Epoch to Date, UTC Offsets & Relative Time

How to convert Unix timestamps to human-readable dates, auto-detect seconds vs milliseconds, apply UTC offsets for local time, and get relative time strings.

25 June 2026 5 min read By Tools.Town Team Fact Checked

Key Takeaways

  • Count the digits
  • Switch to 'Date → Timestamp' mode
  • IST is UTC+5:30
  • Relative time is a human-friendly string like '3 days ago', 'in 2 hours', or '1 year ago'

Modes at a glance

The Unix Timestamp Converter has three modes:

Timestamp → Date: paste a Unix timestamp (seconds or ms), get ISO 8601, UTC string, local string, date components, week number, and relative time.

Date → Timestamp: paste an ISO 8601 string or date-time string, get the Unix timestamp in seconds and milliseconds.

Current Time: shows the live Unix timestamp (updating in real time) plus all formatted representations for right now.

Auto-detecting seconds vs milliseconds

The converter uses this rule: if the numeric value is below 10,000,000,000 (10^10), treat it as seconds. Above that, treat it as milliseconds.

ValueInterpretationDate
1735689600Seconds1 Jan 2025 00:00:00 UTC
1735689600000Milliseconds1 Jan 2025 00:00:00 UTC
0Seconds1 Jan 1970 (Unix epoch)

If the auto-detection is wrong (e.g. you have a seconds timestamp > 10^10 in the far future), you can pre-divide or pre-multiply manually.

UTC offsets

The UTC Offset dropdown covers every half-hour step from UTC−12:00 to UTC+14:00. Selecting UTC+05:30 for IST shifts the “Local string” display by 5.5 hours ahead of UTC.

Note: UTC offset is not the same as your browser’s local timezone. The offset is applied manually (UTC timestamp + offset hours → local display), so daylight saving is not automatically handled. Use the Timezone Converter for DST-aware conversions.

Output formats

OutputExample
Unix seconds1735689600
Unix milliseconds1735689600000
ISO 86012025-01-01T00:00:00.000Z
UTC stringWed, 01 Jan 2025 00:00:00 GMT
Short date1 Jan 2025
Long dateWednesday, 1 January 2025 at 00:00:00 UTC
Relative time6 months ago

Common use cases

Debugging API responses: JSON payloads often contain created_at: 1735689600. Paste it into Timestamp → Date mode to verify it’s the expected date.

Generating test timestamps: switch to Date → Timestamp mode, enter a reference date, copy the Unix timestamp to use in test fixtures.

Log analysis: server logs often use Unix seconds. Paste a range of timestamps to confirm they fall within the expected window.

Scheduling checks: verify that a scheduled task (cron job, delayed queue message) fires at the correct moment by checking its trigger timestamp.

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Frequently Asked Questions

How do I know if a timestamp is in seconds or milliseconds?
Count the digits. A timestamp of 10 digits (e.g. 1735689600) is in seconds. 13 digits (e.g. 1735689600000) is milliseconds. The converter auto-detects: values below 10^10 are treated as seconds.
How do I convert a date to a Unix timestamp?
Switch to 'Date → Timestamp' mode. Paste an ISO 8601 string like '2025-01-01T00:00:00Z' or a date-time string like '2025-01-01 12:30:00'. The converter returns the Unix timestamp in both seconds and milliseconds.
What UTC offset should I use for IST?
IST is UTC+5:30. In the UTC Offset dropdown, select UTC+05:30. This shifts the displayed local time by 5.5 hours ahead of UTC.
What is relative time?
Relative time is a human-friendly string like '3 days ago', 'in 2 hours', or '1 year ago'. It's computed by comparing the timestamp to the current time. Useful for sanity-checking whether a timestamp is in the past or future.

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