How to fix: Unix timestamp in seconds vs milliseconds

Unix timestamps come in two flavors: seconds since epoch (10 digits) and milliseconds (13 digits). Using the wrong unit produces wildly wrong dates. Fix: 1. Check digit count: 10 digits = seconds, 13 digits = milliseconds. 2. Use our Timestamp Converter to test both formats. 3. In JavaScript, Date.now() returns milliseconds; divide by 1000 for seconds. 4. In Python, time.time() returns seconds; multiply by 1000 for milliseconds.

How to fix: Timezone mismatch between server and client

Storing or transmitting timestamps without timezone information leads to ambiguity. A timestamp of 2024-04-16 10:00:00 could mean UTC, EST, PST, or any other timezone. Fix: 1. Convert the timestamp in our Timestamp Converter and check the timezone display. 2. Store all timestamps in UTC on the backend. 3. Include timezone in ISO 8601 format: 2024-04-16T10:00:00Z (Z = UTC). 4. Convert to local timezone only on the client side for display.

How to fix: Daylight Saving Time (DST) causes off-by-one-hour

DST transitions create hours that do not exist (spring forward) or repeat (fall back). Naive timezone handling breaks during these transitions. Fix: 1. Always store and compute times in UTC - convert to local only for display. 2. Use timezone-aware libraries (Luxon, date-fns-tz, pytz/zoneinfo). 3. Test with timestamps near DST transitions. 4. Use our Timestamp Converter to verify conversions around DST boundaries.

Data Formats 2026-04-16

Fix Timestamp Conversion & Timezone Errors

Debug Unix timestamp issues: milliseconds vs seconds confusion, timezone mismatches, daylight saving time errors, and date parsing failures.

⏱ Unix Timestamp Converter Free

timestamp wrong timezone unix timestamp not working date parsing error epoch time conversion error

Timestamp bugs are among the sneakiest in software: they work fine during testing but break in production across timezones. This guide covers the most common timestamp and timezone issues.

Common errors covered

1 Unix timestamp in seconds vs milliseconds
2 Timezone mismatch between server and client
3 Daylight Saving Time (DST) causes off-by-one-hour

Unix timestamp in seconds vs milliseconds

Error message

Date shows as January 1970 instead of current date
Date shows as year 53000+ (far future)

Root cause

Unix timestamps come in two flavors: seconds since epoch (10 digits) and milliseconds (13 digits). Using the wrong unit produces wildly wrong dates.

Step-by-step fix

1 Check digit count: 10 digits = seconds, 13 digits = milliseconds.
2 Use our Timestamp Converter to test both formats.
3 In JavaScript, Date.now() returns milliseconds; divide by 1000 for seconds.
4 In Python, time.time() returns seconds; multiply by 1000 for milliseconds.

Wrong

// JavaScript expects milliseconds, but got seconds
new Date(1713264000)
// Result: Mon Jan 20 1970 (wrong!)

Correct

// Multiply seconds by 1000 for JavaScript
new Date(1713264000 * 1000)
// Result: Tue Apr 16 2024 (correct!)

Timezone mismatch between server and client

Error message

Event shows at wrong time for users in different timezones
Scheduled task runs hours early/late

Root cause

Storing or transmitting timestamps without timezone information leads to ambiguity. A timestamp of 2024-04-16 10:00:00 could mean UTC, EST, PST, or any other timezone.

Step-by-step fix

1 Convert the timestamp in our Timestamp Converter and check the timezone display.
2 Store all timestamps in UTC on the backend.
3 Include timezone in ISO 8601 format: 2024-04-16T10:00:00Z (Z = UTC).
4 Convert to local timezone only on the client side for display.

Wrong

// Ambiguous: which timezone?
const event = '2024-04-16 10:00:00';
new Date(event);  // Interpreted differently per browser!

Correct

// Explicit UTC timestamp
const event = '2024-04-16T10:00:00Z';
new Date(event);  // Always UTC, convert for display

Daylight Saving Time (DST) causes off-by-one-hour

Error message

Daily job runs at wrong time twice a year
Timestamps shift by 1 hour on specific dates

Root cause

DST transitions create hours that do not exist (spring forward) or repeat (fall back). Naive timezone handling breaks during these transitions.

Step-by-step fix

1 Always store and compute times in UTC - convert to local only for display.
2 Use timezone-aware libraries (Luxon, date-fns-tz, pytz/zoneinfo).
3 Test with timestamps near DST transitions.
4 Use our Timestamp Converter to verify conversions around DST boundaries.

Wrong

# Naive datetime loses DST info
from datetime import datetime
dt = datetime(2024, 3, 10, 2, 30)  # This time may not exist!

Correct

# Timezone-aware datetime handles DST
from datetime import datetime
from zoneinfo import ZoneInfo
dt = datetime(2024, 3, 10, 2, 30, tzinfo=ZoneInfo('US/Eastern'))

Prevention Tips

Store all timestamps as UTC Unix timestamps or ISO 8601 with timezone.
Use Date.now() (JS) or time.time() (Python) for current timestamps.
Test your application with different system timezones before deployment.
Use our Timestamp Converter to validate conversions during development.

Frequently Asked Questions

What is Unix epoch time?

Unix epoch is January 1, 1970, 00:00:00 UTC. A Unix timestamp is the number of seconds (or milliseconds) since that moment. It is timezone-independent, making it ideal for storing and comparing times.

Why does Date.parse give different results in different browsers?

Date string parsing is one of the most inconsistent parts of JavaScript. Always use ISO 8601 format (2024-04-16T10:00:00Z) for reliable cross-browser parsing.

Should I use seconds or milliseconds for timestamps?

Most backend systems (Python, databases, Unix) use seconds. JavaScript uses milliseconds. APIs vary. Document which unit your system uses and convert at boundaries.