Converting Epoch to Human Date

Converting a Unix epoch timestamp to a human-readable date is one of the most frequent operations in programming. The process involves taking the number of seconds (or milliseconds) since January 1, 1970 UTC and translating it into a year, month, day, hour, minute, and second representation.

Conversions in every major language:

// JavaScript (input: milliseconds)
new Date(1704067200 * 1000).toISOString()
// "2024-01-01T00:00:00.000Z"

new Date(1704067200 * 1000).toLocaleString("en-US", {
  timeZone: "America/New_York"
})
// "12/31/2023, 7:00:00 PM"

# Python
from datetime import datetime, timezone
datetime.fromtimestamp(1704067200, tz=timezone.utc)
# datetime(2024, 1, 1, 0, 0, tzinfo=timezone.utc)

// Java
Instant.ofEpochSecond(1704067200L)
    .atZone(ZoneId.of("UTC"))
    .format(DateTimeFormatter.ISO_DATE_TIME)
// "2024-01-01T00:00:00Z"

// Go
time.Unix(1704067200, 0).UTC().Format(time.RFC3339)
// "2024-01-01T00:00:00Z"

-- MySQL
SELECT FROM_UNIXTIME(1704067200);  -- '2024-01-01 00:00:00'

-- PostgreSQL
SELECT to_timestamp(1704067200);   -- '2024-01-01 00:00:00+00'

# Linux/macOS
date -d @1704067200              # Linux
date -r 1704067200               # macOS

Key considerations:

Always know whether your input timestamp is in seconds or milliseconds. JavaScript's Date constructor expects milliseconds, so you must multiply seconds by 1000. Getting this wrong produces a date in January 1970 instead of the expected date.

Timezone matters on output: The same timestamp produces different readable dates depending on the timezone you apply. 1704067200 is midnight January 1, 2024 in UTC, but it is 7:00 PM on December 31, 2023 in New York. Always specify the desired timezone explicitly in your formatting call.

Batch conversions: When converting many timestamps (e.g., processing log files), create the formatter or timezone object once outside the loop rather than on every iteration. This can be 10-100x faster depending on the language.