Unix Timestamp Conversion: Complete Guide

Introduction

Timestamps are numeric representations of dates and times, essential for logging, scheduling, and data synchronization. Understanding timestamp formats and conversions is crucial for backend development and API integration.

This guide covers Unix timestamps, ISO 8601, and common conversion scenarios.

Unix Timestamp

Unix time counts seconds since January 1, 1970 00:00:00 UTC (the Unix epoch):

// Unix timestamp (seconds)
  1704067200  // January 1, 2024 00:00:00 UTC

  // Milliseconds (JavaScript)
  1704067200000

  // Current timestamp
  const now = Math.floor(Date.now() / 1000);
  // Result: 1707321600 (example)

Format: Integer (seconds or milliseconds)
Timezone: Always UTC
Range: Signed 32-bit: 1901-2038, 64-bit: billions of years

ISO 8601 Format

ISO 8601 is a human-readable international standard:

// Basic format
  2024-01-01T00:00:00Z

  // With timezone offset
  2024-01-01T08:00:00+08:00

  // Milliseconds
  2024-01-01T00:00:00.123Z

  // Date only
  2024-01-01

T: Separates date and time
Z: Indicates UTC ("Zulu" time)
+/-HH:MM: Timezone offset from UTC

Common Conversions

Unix to ISO 8601 (JavaScript):

// From seconds
  const timestamp = 1704067200;
  const date = new Date(timestamp * 1000);
  const iso = date.toISOString();
  // Result: "2024-01-01T00:00:00.000Z"

  // From milliseconds
  const ms = 1704067200000;
  const iso = new Date(ms).toISOString();
  // Result: "2024-01-01T00:00:00.000Z"

ISO to Unix (JavaScript):

const iso = "2024-01-01T00:00:00.000Z";
  const timestamp = Math.floor(new Date(iso).getTime() / 1000);
  // Result: 1704067200

Python:

import datetime

  # Unix to ISO
  timestamp = 1704067200
  dt = datetime.datetime.fromtimestamp(timestamp, tz=datetime.timezone.utc)
  iso = dt.isoformat()
  # Result: '2024-01-01T00:00:00+00:00'

  # ISO to Unix
  iso = "2024-01-01T00:00:00Z"
  dt = datetime.datetime.fromisoformat(iso.replace('Z', '+00:00'))
  timestamp = int(dt.timestamp())
  # Result: 1704067200

Timezone Handling

Always be explicit about timezones:

// UTC (Recommended for storage)
  2024-01-01T00:00:00Z

  // US Eastern Time (UTC-5)
  2024-01-01T00:00:00-05:00

  // Tokyo (UTC+9)
  2024-01-01T00:00:00+09:00

  // Convert to user's timezone on display
  const utc = "2024-01-01T00:00:00Z";
  const local = new Date(utc).toLocaleString();
  // Result: "1/1/2024, 8:00:00 AM" (if user is UTC+8)

Common Pitfalls

Seconds vs Milliseconds: JavaScript uses ms, most systems use seconds
Timezone confusion: Always store in UTC, convert for display
Year 2038 problem: 32-bit timestamps overflow on Jan 19, 2038
Leap seconds: Not handled by Unix time
Local time: Avoid storing local time without timezone info

Best Practices

Store timestamps in UTC
Use 64-bit integers for Unix timestamps
Use ISO 8601 for human-readable formats
Always include timezone in ISO format
Convert to user's timezone only for display
Use database timestamp types (not strings)
Test with different timezones and DST transitions

Database Examples

-- PostgreSQL
  CREATE TABLE events (
    id SERIAL PRIMARY KEY,
    created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
    updated_at TIMESTAMP WITH TIME ZONE
  );

  -- Query with timezone
  SELECT
    created_at AT TIME ZONE 'UTC' as utc_time,
    created_at AT TIME ZONE 'America/New_York' as ny_time
  FROM events;

  -- MySQL
  CREATE TABLE logs (
    id INT PRIMARY KEY,
    timestamp TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    datetime DATETIME
  );

Try Our Tools

Explore our free online developer tools:

Timestamp Converter