What is the best format for displaying times internationally?

The Challenge of International Time Display

Displaying time to an international audience is more complex than it appears. While Americans expect times like "2:30 PM," Europeans expect "14:30," and other regions have their own conventions. What seems like a simple formatting problem becomes complicated when you need to handle different locales, timezones, daylight saving time, and various date/time conventions.

The goal isn't just to show the correct time, but to show it in a way that's unambiguous, accessible to the intended audience, and technically correct across timezone boundaries. This requires understanding international conventions and implementing proper localization in your application.

ISO 8601: The International Standard

ISO 8601 is the international standard for date and time representation. It's the starting point for any international time display strategy.

ISO 8601 Format:

2024-01-15T14:30:45Z (UTC)
2024-01-15T14:30:45+05:30 (with timezone offset)
2024-01-15T14:30:45-08:00 (negative offset)
2024-01-15T14:30:45.123Z (with milliseconds)
2024-01-15T14:30:45+05:30[Asia/Kolkata] (with timezone identifier)

Key features:

• Date in YYYY-MM-DD format (unambiguous, no regional variations)
• Time in HH:MM:SS format (24-hour, unambiguous)
• "T" separating date and time
• "Z" indicating UTC, or +/- offset indicating timezone

Why ISO 8601:

• Unambiguous (no confusion about 01/02/2024 being January or February)
• Sortable as strings (chronologically ordered)
• Parseable by all modern languages and systems
• International standard that eliminates regional assumptions

Best Practices for Different Contexts

For Machine-Readable Data (APIs, Databases): Always use ISO 8601 with UTC timezone:

{
  "eventTime": "2024-01-15T19:30:00Z",
  "userTimezone": "America/New_York"
}

This ensures data is unambiguous and transferable between systems.

For User-Facing Display in Web Applications: Display the time in the user's local timezone with clear timezone information:

In English-speaking regions:

2:30 PM EST (January 15, 2024)
or
Jan 15, 2:30 PM Eastern Time

In ISO 8601-using regions (most of the world):

15:30 CET (15 janvier 2024)
or
15. Januar, 15:30 Mitteleuropäische Zeit

For Logs and Timestamps: Use ISO 8601 with timezone offset, sortable format:

2024-01-15T14:30:45.123-08:00

This is human-readable and machine-parseable while preserving timezone information.

Regional Time Format Variations

12-Hour vs 24-Hour Time:

• 12-hour format (with AM/PM): United States, Canada, Philippines, Australia (some regions)
• 24-hour format: Most of Europe, Latin America, Asia, Australia (some regions)

Your application should detect the user's locale and format accordingly.

Date Format Variations:

• MM/DD/YYYY: United States
• DD/MM/YYYY: Most of Europe, Latin America, Australia
• YYYY-MM-DD: ISO 8601 (best for international)

Avoid abbreviations and use month names when possible:

January 15, 2024 (clear everywhere)
vs
01/15/2024 (ambiguous—is this January 15 or May 1?)

Timezone Representation:

• Abbreviations (EST, PST, GMT): Ambiguous and can be confused (EST vs EDT)
• Offset (+05:30, -08:00): Precise
• Timezone name (America/New_York, Europe/London): Precise

Best practice: Include both the offset and timezone name when space allows.

Implementation Strategies

JavaScript/Node.js Example:

const { DateTime } = require('luxon');

// Parse timestamp and convert to user timezone
const utcTime = DateTime.fromISO("2024-01-15T19:30:00Z");
const userTimezone = "America/New_York"; // From user profile
const localTime = utcTime.setZone(userTimezone);

// Format for display
const formatted = localTime.toLocaleString(
  DateTime.DATETIME_FULL_WITH_SECONDS
);
console.log(formatted); // "January 15, 2024, 2:30:45 PM"

// Include timezone info
const withTz = `${formatted} ${localTime.zoneName}`;
console.log(withTz); // "January 15, 2024, 2:30:45 PM EST"

// For user's locale
const userLocale = "en-US"; // or "de-DE", "fr-FR", etc.
const localizedTime = localTime.toLocaleString(
  DateTime.DATETIME_FULL,
  { locale: userLocale }
);
console.log(localizedTime);

Python Example:

from datetime import datetime
import pytz
from babel.dates import format_datetime

# Parse UTC time
utc_time = datetime(2024, 1, 15, 19, 30, 0, tzinfo=pytz.UTC)

# Convert to user timezone
user_tz = pytz.timezone("America/New_York")
local_time = utc_time.astimezone(user_tz)

# Format for display (US English)
formatted = format_datetime(local_time, format='EEEE, MMMM d, y, h:mm:ss a zzz', locale='en_US')
print(formatted)  # "Monday, January 15, 2024, 2:30:45 PM EST"

# Format for different locale (German)
formatted_de = format_datetime(local_time, format='EEEE, d. MMMM y, HH:mm:ss zzz', locale='de_DE')
print(formatted_de)  # "Montag, 15. Januar 2024, 14:30:45 EST"

React Example:

import { DateTime } from 'luxon';

function TimeDisplay({ utcTime, userTimezone, userLocale }) {
  const localTime = DateTime.fromISO(utcTime).setZone(userTimezone);

  // Format based on user locale
  const formatted = localTime.toLocaleString(
    DateTime.DATETIME_FULL_WITH_SECONDS,
    { locale: userLocale }
  );

  return (
    <time dateTime={utcTime}>
      {formatted}
      <span className="timezone"> {localTime.zoneName}</span>
    </time>
  );
}

Handling Ambiguity

When Times Are Ambiguous (during daylight saving transitions): If you must display a time that's ambiguous (occurs twice when clocks fall back), include additional context:

November 5, 2023, 1:30 AM EDT (before transition)
or
November 5, 2023, 1:30 AM EST (after transition)

Better: Use the full ISO 8601 with offset to remove ambiguity:

2023-11-05T01:30:00-04:00
2023-11-05T01:30:00-05:00

When Displaying to Multiple Timezone Audiences: If a time matters to people in multiple timezones (meeting time, event time), show the time in multiple zones:

Server maintenance window:
Tuesday, January 16, 2024
2:00 AM PST / 5:00 AM EST / 10:00 AM GMT / 3:30 PM IST

Or provide an interactive world clock that automatically shows the time in the user's timezone.

UI/UX Considerations

Provide Timezone Context: Don't assume users know what timezone a time is in:

2:30 PM (EST)  ← Good, includes timezone
2:30 PM        ← Bad, unclear

Use Native Time Elements: In HTML, use the <time> element with datetime attribute:

<time datetime="2024-01-15T14:30:00-05:00">
  January 15, 2:30 PM Eastern Time
</time>

This helps browsers, screen readers, and assistive technology understand the time.

Enable Timezone Conversion: In web applications, let users click a time to see it in their timezone:

<time datetime="2024-01-15T19:30:00Z"
      title="2:30 PM EST (January 15, 2024)"
      onClick={showInMyTimezone}>
  January 15, 2:30 PM EST
</time>

// On click, display modal showing time in user's timezone

Consider Mobile: On mobile devices, space is limited. Display concise but clear times:

2:30 PM EST
(not: Monday, January 15, 2024, 2:30:45 PM Eastern Standard Time)

Localization Libraries

Luxon (JavaScript):

const { DateTime } = require('luxon');
DateTime.now().toLocaleString(DateTime.DATETIME_FULL);

Babel (Python):

from babel.dates import format_datetime
format_datetime(datetime.now(), locale='en_US')

date-fns (JavaScript):

import { format } from 'date-fns';
format(new Date(), 'PPPP p OOOO'); // Locale-aware formatting

Moment-timezone (JavaScript):

moment.tz("2024-01-15 14:30", "YYYY-MM-DD HH:mm", "America/New_York")
  .format('LLLL');

Java java.time:

ZonedDateTime zdt = ZonedDateTime.now(ZoneId.of("America/New_York"));
DateTimeFormatter formatter = DateTimeFormatter.ofLocalizedDateTime(
  FormatStyle.FULL, FormatStyle.MEDIUM
);
String formatted = zdt.format(formatter.withLocale(Locale.ENGLISH));

Common Mistakes to Avoid

1. Assuming everyone uses 12-hour time: They don't. Detect locale.

2. Using timezone abbreviations: EST, PST, GMT are ambiguous. Use full names or offsets.

3. Storing local times without timezone: Always know what timezone a time is in.

4. Not handling daylight saving time: Your library should do this automatically.

5. Displaying times without timezone context: Always indicate the timezone.

6. Forgetting about seconds: 2:30:45 PM is more precise than 2:30 PM.

7. Using locale-unaware formatting: Use libraries that handle localization, not hardcoded strings.

Conclusion

The best format for displaying times internationally involves three principles: (1) Store all times in UTC with ISO 8601 format, (2) Convert to the user's local timezone for display, and (3) Format according to the user's locale using proper localization libraries. This approach ensures your application handles timezones correctly, accommodates users from different regions, and displays times unambiguously. By using established standards like ISO 8601, leveraging localization libraries, and providing clear timezone context, you create time displays that work correctly and intuitively for international audiences.