Understanding Timestamps: ISO, Unix, and RFC Formats

Timestamps show exactly when events happen. They're everywhere—from log files and APIs to database entries—but their multiple formats can confuse even experienced developers.

In this guide, you'll learn:

The differences between ISO 8601, Unix, and RFC 2822 formats.
When and why to use each format.
How to convert timestamps easily using code examples.
Best practices and common pitfalls.

⏰ What Exactly Is a Timestamp?

A timestamp is simply data that records the exact time something occurred. In computing, we use them to:

Track data creation and modification.
Synchronize events across systems.
Debug by correlating system logs.

📅 Common Timestamp Formats Explained

There are three major formats used widely in software development:

1. ISO 8601 Format

An international standard that's clear, sortable, and human-readable.

Examples:


2025-01-08T14:30:00Z
2025-01-08T14:30:00+00:00

Pros:

Human-readable and easy to sort.
Clearly indicates timezones.
Widely supported internationally.

Cons:

Slightly verbose for massive datasets.

2. Unix Timestamp (Epoch Time)

Counts seconds (or milliseconds) from midnight, January 1, 1970 UTC.

Examples:


1704720600 // Seconds
1704720600000 // Milliseconds

Pros:

Compact and efficient.
Easy for calculations and comparisons.

Cons:

Not easily readable without conversion.
No direct timezone information.

3. RFC 2822 Format

Commonly used in email and HTTP headers.

Examples:


Wed, 08 Jan 2025 14:30:00 GMT
Wed, 08 Jan 2025 09:30:00 -0500

Pros:

Human-readable.
Standard in email protocols.

Cons:

Not sortable as text.
Locale-dependent (month names).

🗂️ Quick Reference Table

Feature	ISO 8601	Unix Timestamp	RFC 2822
Human-readable	✅	❌	✅
Compact storage	❌	✅	❌
Sortable	✅	✅ (numeric)	❌
Timezone clarity	✅	❌	✅
Usage context	APIs, logs	Databases, apps	Email, HTTP

🛠️ When to Use Each Format

ISO 8601: APIs, logs, international apps.
Unix Timestamp: Databases, performance-critical apps.
RFC 2822: Emails, HTTP headers, legacy systems.

⚙️ How to Convert Between Formats

Use the examples below to quickly convert timestamps in your applications.

JavaScript

// ISO 8601 to Unix timestamp
const isoDate = "2025-01-08T14:30:00Z";
const unixTimestamp = Date.parse(isoDate) / 1000;

// Unix timestamp to ISO 8601
const timestamp = 1704720600;
const isoString = new Date(timestamp * 1000).toISOString();

// RFC 2822 to ISO 8601
const rfcDate = "Wed, 08 Jan 2025 14:30:00 GMT";
const isoFromRfc = new Date(rfcDate).toISOString();

Python

from datetime import datetime, timezone

# ISO 8601 to Unix timestamp
iso_date = '2025-01-08T14:30:00Z'
dt = datetime.fromisoformat(iso_date.replace('Z', '+00:00'))
unix_timestamp = dt.timestamp()

# Unix timestamp to ISO 8601
timestamp = 1704720600
iso_string = datetime.fromtimestamp(timestamp, tz=timezone.utc).isoformat()

# RFC 2822 to ISO 8601
from email.utils import parsedate_to_datetime
rfc_date = 'Wed, 08 Jan 2025 14:30:00 GMT'
iso_from_rfc = parsedate_to_datetime(rfc_date).isoformat()