WordPress Locale, Dates & Numbers

WP's date/time API has TWO eras: pre-5.3 (offset-summed timestamps, date_i18n, current_time('timestamp') — quirky, error-prone) and 5.3+ (true UTC timestamps, DateTimeZone objects, wp_date, current_datetime). Most plugins still write pre-5.3 code because that's what AI training data is full of. This skill is the modern recipe.

When to use this skill

Trigger when ANY of the following is true:

A plugin stores, queries, or displays dates / times — scheduled tasks, expiry dates, audit timestamps, log entries, "X minutes ago" labels, REST date fields.
Code references wp_date, current_datetime, current_time, date_i18n, wp_timezone, wp_timezone_string, get_gmt_from_date, get_date_from_gmt, mysql2date, mysql_to_rfc3339, iso8601_to_datetime, number_format_i18n.
Code calls time(), date(), strtotime() directly for site-display dates without considering timezone.
The user reports: "wrong timezone on schedule emails", "WP-Admin shows EST but database has UTC", "Friday in Europe shows as Thursday in REST".

The mental model — timestamps are UTC, formatting is local

Since WP 5.3, the rule is:

Timestamps stored in code (and Unix epoch in general) are UTC integers. time() returns UTC. wp_date() accepts UTC and formats in a target timezone.
Core post date fields are paired by convention: post_date is site-local and post_date_gmt is UTC. This does not mean every WordPress/plugin DATETIME is implicitly local; a SQL DATETIME has no timezone metadata.
The "site's timezone" is configurable — Settings → General → Timezone. It's either Europe/Budapest (IANA name in timezone_string) or a manual +02:00 offset (in gmt_offset). Use wp_timezone() / wp_timezone_string() — they handle the fallback for you (wp-includes/functions.php:124-154).

Always reach for these (modern API)

Need	Function	Notes
Current UTC timestamp	`time()`	Plain PHP. WP doesn't wrap.
Current local DateTimeImmutable	`current_datetime()`	Site timezone (5.3+)
Format a UTC timestamp for display	`wp_date( $format, $timestamp = null, $timezone = null )`	Default timezone = site. Default timestamp = now. Returns `false` on invalid input
Site timezone object	`wp_timezone()`	Returns `DateTimeZone`, never null
Site timezone string	`wp_timezone_string()`	IANA name OR `±HH:MM` offset
Convert site-local datetime → UTC	`get_gmt_from_date( $date_string, $format = 'Y-m-d H:i:s' )`	Takes a `Y-m-d H:i:s` string in site TZ, returns UTC. Validate input first
Convert UTC datetime → site-local	`get_date_from_gmt( $date_string, $format = 'Y-m-d H:i:s' )`	Mirror image. Validate input first
Locale-aware number	`number_format_i18n( $number, $decimals = 0 )`	Reads `$wp_locale->number_format['decimal_point' \| 'thousands_sep']`

Avoid these unless interfacing with legacy code

current_time( 'timestamp' ) — returns time() + gmt_offset * 3600. The result is NOT a real Unix timestamp — it's UTC summed with the site's offset. Pre-5.3 code uses it to feed date() directly. PHPCS flags it via WordPress.DateTime.CurrentTimeTimestamp.Requested. Use time() for UTC or current_datetime()->getTimestamp() for a proper local-now-as-UTC-int.
date_i18n( $format, $timestamp_with_offset ) — legacy wrapper around wp_date. Same trap as above: the $timestamp arg expects offset-summed values, not real UTC. wp_date is the cleaner replacement (wp-includes/functions.php:179).
mysql_to_rfc3339( $date_string ) — function name lies: source docblock explicitly says "the output does NOT conform to RFC3339 format, which must contain timezone" (wp-includes/functions.php:7855). It outputs Y-m-d\TH:i:s with no Z / no offset. Use it only if you specifically want WP's REST-compatible "local without offset" shape (that's the convention for REST *_gmt fields, despite the misleading name).

Storing dates

MySQL DATETIME columns

For new plugin tables, prefer one canonical UTC instant: a UTC DATETIME or a Unix integer. Add a site-local companion only when interoperating with a core schema/pattern or when a demonstrated local-time query/display requirement justifies the duplication. Document the timezone semantics in the column name and schema comments.

$now_utc = current_datetime()->setTimezone( new DateTimeZone( 'UTC' ) );

$wpdb->insert( $wpdb->prefix . 'myplugin_events', array(
    'event_date_gmt' => $now_utc->format( 'Y-m-d H:i:s' ),
) );

If you only have a user-entered local date string (e.g. from a datepicker — see wp-admin-form-controls), convert at the boundary:

$user_input = '2026-06-01 14:30:00';                      // assumed in site TZ
$gmt_string = get_gmt_from_date( $user_input );           // → 'Y-m-d H:i:s' in UTC

get_gmt_from_date() and get_date_from_gmt() are converters, not validators. On parse failure core returns gmdate( $format, 0 ) (usually 1970-01-01 00:00:00), so validate user input before conversion.

Local date-times can also be nonexistent or ambiguous across DST transitions. For exact scheduling, parse with wp_timezone(), round-trip the formatted value to detect normalization through a DST gap, and define a product policy for repeated local times (ask for an offset/occurrence or reject ambiguity). Date-only values do not identify an instant and should remain Y-m-d when that is the real domain value.

Storage as Unix integer

For event timestamps, expiry, etc., store as a BIGINT UTC integer (time()). Simple to query (WHERE expires_at < UNIX_TIMESTAMP()), no timezone ambiguity. Display-side, feed to wp_date().

$row = array( 'expires_at' => time() + DAY_IN_SECONDS * 30 );
// ...
$display = wp_date( get_option( 'date_format' ) . ' ' . get_option( 'time_format' ), $row['expires_at'] );

get_option( 'date_format' ) and get_option( 'time_format' ) are the user-configured formats from Settings → General. Use them so a German site shows 01.06.2026 and a US one shows 06/01/2026.

Display

// Now, in site timezone, with site's date format.
echo esc_html( wp_date( get_option( 'date_format' ) ) );

// A stored UTC timestamp, shown in site timezone (default).
echo esc_html( wp_date( 'Y-m-d H:i', $expires_at_int ) );

// Same timestamp, but force UTC display.
echo esc_html( wp_date( 'Y-m-d H:i', $expires_at_int, new DateTimeZone( 'UTC' ) ) );

// Localized numbers.
echo esc_html( number_format_i18n( 1234567.89, 2 ) );    // de_DE: "1.234.567,89"

wp_date localizes day/month names via $wp_locale, but it does not rearrange your format string. Use the site's date_format / time_format options for normal UI instead of hardcoding English-style ordering.

REST API dates

WP REST returns dates as *_gmt and * fields. The _gmt field uses the mysql_to_rfc3339 shape (no Z/offset — confusing but it's the convention). Don't try to fight it; emit the same shape from your custom REST routes:

// In a REST callback that builds a response:
$response_data = array(
    'created_at'     => mysql_to_rfc3339( get_date_from_gmt( $row['created_at_gmt'] ) ),
    'created_at_gmt' => mysql_to_rfc3339( $row['created_at_gmt'] ),
);

For genuine ISO 8601 with offset (needed if a third-party API expects RFC3339-compliant), use DateTimeImmutable::format( DateTimeInterface::ATOM ) (= 'Y-m-d\TH:i:sP') directly.

Locale-aware numbers

number_format_i18n( $number, $decimals = 0 ) uses $wp_locale->number_format['decimal_point'] and ['thousands_sep'] (verified at wp-includes/functions.php:424). It does NOT do currency formatting — that's WC's wc_price() territory. For non-WC currency display, build your own around number_format_i18n + a currency symbol option.

$total = 1234.5;
$displayed = number_format_i18n( $total, 2 ) . ' ' . esc_html( get_option( 'myplugin_currency_symbol', 'USD' ) );

Locale file loading

Translation loading is its own topic — see wp-i18n-audit. $wp_locale is initialized during core bootstrap, but plugins should not render user-facing dates at file-load time. Generate UI on its normal lifecycle hook (init or a later render hook), after locale and plugin translation setup is available.

Critical rules

Treat time() results as UTC integers. Pass them to wp_date() for display in site timezone, or gmdate() for UTC display. NEVER add the site offset to a time() value before formatting — that's the legacy current_time('timestamp') foot-gun.
current_time( 'timestamp' ) is NOT a Unix timestamp. It's time() + offset * 3600. PHPCS flags it. The correct replacement: current_datetime() for an object, time() for UTC int.
mysql_to_rfc3339() does NOT produce RFC3339. The function name is wrong; it produces ISO 8601 without timezone. Source explicitly notes this. Use it for REST compatibility; use DateTimeInterface::ATOM for actually-RFC3339-compliant output.
Prefer one canonical UTC instant in custom tables. Use paired local/UTC columns only for a documented interoperability or query requirement; when a local column exists, keep its UTC companion authoritative and synchronized.
wp_timezone_string() may return an IANA name OR a ±HH:MM offset. Don't assume IANA — sites with gmt_offset set but no timezone_string produce the offset form. DateTimeZone() accepts both, so use wp_timezone() (object) whenever possible.
Use get_option('date_format') + get_option('time_format') for user-facing display, not hardcoded 'Y-m-d'. Respects the site admin's preference.
Don't store locale-formatted strings. Store machine values (Y-m-d H:i:s or UTC integers), then format at display. Locale-shaped strings are hard to query and migrate.
Do not render user-facing dates at plugin file load. Use the normal init-or-later application/render lifecycle so locale setup is complete.

Common AI mistakes

// WRONG — uses pre-5.3 quirk; result is NOT a real Unix timestamp
$ts = current_time( 'timestamp' );
echo date( 'Y-m-d H:i', $ts );

// RIGHT — modern path
echo esc_html( wp_date( 'Y-m-d H:i' ) );

// WRONG — date() in PHP uses server's PHP timezone (often UTC), not site's WP timezone
echo date( 'Y-m-d H:i', $created_at );

// RIGHT — wp_date respects site timezone setting
echo esc_html( wp_date( 'Y-m-d H:i', $created_at ) );

// WRONG — adding offset to a UTC time twice; ends up double-shifted
$shifted = time() + (int) get_option( 'gmt_offset' ) * HOUR_IN_SECONDS;
echo date( 'H:i', $shifted );

// RIGHT — wp_date handles the timezone shift internally
echo esc_html( wp_date( 'H:i' ) );

// WRONG — assumes IANA timezone; breaks when site uses gmt_offset
$tz = new DateTimeZone( get_option( 'timezone_string' ) );

// RIGHT — wp_timezone falls back to gmt_offset
$tz = wp_timezone();

// WRONG — function name lies; produces ISO 8601 without TZ, NOT RFC3339
$rfc3339 = mysql_to_rfc3339( $datetime_string );  // for external API: WRONG

// RIGHT — actually-RFC3339
$rfc3339 = ( new DateTimeImmutable( $datetime_string, wp_timezone() ) )
    ->format( DateTimeInterface::ATOM );

Cross-references

See wp-i18n-audit for translation loading order — relevant because $wp_locale->month / weekday content depends on textdomain being loaded.
See wp-admin-form-controls for the datepicker that emits Y-m-d strings, and the sanitize-callback strict validation that matches them.
See wp-rest-api when emitting date fields in REST responses — match the *_gmt convention.

What this skill does NOT cover

Currency formatting. number_format_i18n formats numbers; currency display (locale-aware position of symbol, locale-specific separators) is its own topic. WC has wc_price(); non-WC plugins build a small wrapper.
Custom calendar (Hijri, Buddhist, Jalali). WP only ships Gregorian. Use a third-party calendar library.
Recurring schedules — see wp-plugin-cron + Action Scheduler skills.

References

wp-includes/functions.php:78 — current_time(), including the PHPCS-flagged 'timestamp' branch.
wp-includes/functions.php:101 — current_datetime() (5.3+, returns DateTimeImmutable).
wp-includes/functions.php:124 — wp_timezone_string() with timezone_string → gmt_offset fallback.
wp-includes/functions.php:152 — wp_timezone().
wp-includes/functions.php:179 — date_i18n() (legacy wrapper around wp_date).
wp-includes/functions.php:243 — wp_date() (the modern entry point).
wp-includes/functions.php:424 — number_format_i18n().
wp-includes/functions.php:7863 — mysql_to_rfc3339() with the "does NOT conform to RFC3339" docblock note.
wp-includes/formatting.php:3670 / :3692 — get_gmt_from_date() / get_date_from_gmt().
Official documentation: https://developer.wordpress.org/reference/functions/wp_date/
Official documentation: https://developer.wordpress.org/reference/functions/current_datetime/
Official documentation: https://developer.wordpress.org/reference/functions/wp_timezone/
Official documentation: https://make.wordpress.org/core/2019/09/23/date-time-improvements-wp-5-3/

wp-locale-and-dates

SKILL.mdwordpress/wp-locale-and-dates/SKILL.md