How to Convert a Unix Timestamp to a Human-Readable Date

The core concept

A Unix timestamp counts seconds from the epoch (January 1, 1970 UTC). To display it as a date you need to: (1) multiply by 1000 if your runtime expects milliseconds, (2) pass the value to the platform's date object or function, (3) choose a timezone for display, and (4) format the result into a string.

Steps 1 and 3 are the most common sources of bugs. A 10-digit timestamp is always in seconds; a 13-digit one is in milliseconds. The timezone only changes the display — the underlying moment is the same everywhere on Earth.

JavaScript / TypeScript

The Date constructor expects milliseconds, so multiply seconds by 1000.

const ts = 1735689600; // seconds
const date = new Date(ts * 1000);

// UTC string
console.log(date.toUTCString());
// → "Wed, 01 Jan 2025 00:00:00 GMT"

// ISO 8601
console.log(date.toISOString());
// → "2025-01-01T00:00:00.000Z"

// Locale-aware with timezone
console.log(date.toLocaleString('en-US', {
  timeZone: 'America/New_York',
  dateStyle: 'long',
  timeStyle: 'short'
}));
// → "January 1, 2025 at 7:00 PM"

// Intl.DateTimeFormat for full control
const fmt = new Intl.DateTimeFormat('en-GB', {
  timeZone: 'Europe/Paris',
  year: 'numeric', month: '2-digit', day: '2-digit',
  hour: '2-digit', minute: '2-digit', second: '2-digit',
  hour12: false
});
console.log(fmt.format(date));
// → "01/01/2025, 01:00:00"

Python

Use datetime.utcfromtimestamp() for UTC or datetime.fromtimestamp(ts, tz) to apply a timezone.

from datetime import datetime, timezone, timedelta

ts = 1735689600

# UTC
dt_utc = datetime.fromtimestamp(ts, tz=timezone.utc)
print(dt_utc.isoformat())
# → 2025-01-01T00:00:00+00:00

# With zoneinfo (Python 3.9+)
from zoneinfo import ZoneInfo
dt_paris = datetime.fromtimestamp(ts, tz=ZoneInfo("Europe/Paris"))
print(dt_paris.strftime("%A %d %B %Y %H:%M:%S %Z"))
# → Wednesday 01 January 2025 01:00:00 CET

# Custom format
print(dt_utc.strftime("%Y-%m-%d %H:%M:%S"))
# → 2025-01-01 00:00:00

PHP

$ts = 1735689600;

// Simple: gmdate for UTC, date for server local time
echo gmdate('Y-m-d H:i:s', $ts);   // 2025-01-01 00:00:00 UTC
echo date('Y-m-d H:i:s', $ts);     // server timezone

// With DateTimeImmutable and specific timezone
$dt = (new DateTimeImmutable())->setTimestamp($ts)->setTimezone(new DateTimeZone('America/New_York'));
echo $dt->format('l, F j, Y g:i A');
// → Tuesday, December 31, 2024 7:00 PM

SQL (PostgreSQL & MySQL)

-- Seconds timestamp to timestamptz
SELECT to_timestamp(1735689600) AT TIME ZONE 'Europe/Paris';
-- → 2025-01-01 01:00:00

-- Format it
SELECT to_char(to_timestamp(1735689600), 'YYYY-MM-DD HH24:MI:SS TZ');
-- → 2025-01-01 00:00:00 UTC

SELECT FROM_UNIXTIME(1735689600);
-- → 2025-01-01 00:00:00 (server timezone)

SELECT CONVERT_TZ(FROM_UNIXTIME(1735689600), '+00:00', 'America/New_York');
-- → 2024-12-31 19:00:00

Go

package main

import (
    "fmt"
    "time"
)

func main() {
    ts := int64(1735689600)
    t := time.Unix(ts, 0).UTC()

    fmt.Println(t.Format(time.RFC3339))         // 2025-01-01T00:00:00Z
    fmt.Println(t.Format("2006-01-02 15:04:05")) // 2025-01-01 00:00:00

    loc, _ := time.LoadLocation("America/New_York")
    tNY := t.In(loc)
    fmt.Println(tNY.Format(time.RFC1123Z))       // Tue, 31 Dec 2024 19:00:00 -0500
}

Common mistakes to avoid

• Passing seconds to a milliseconds API. In JavaScript, new Date(1735689600) gives January 21, 1970 — not 2025. Always multiply by 1000.
• Ignoring timezone. date() in PHP and datetime.fromtimestamp() in Python without a tz argument both use the server's local timezone, which may differ from the user's.
• Storing dates as strings in databases. Store as an integer or a native timestamp type and format for display in the application layer.
• Confusing local time input with UTC. When building a timestamp from a form input, ensure you account for the user's timezone offset before converting.