Timestamp & Timezone Converter

A Unix timestamp in seconds is a 10-digit number (e.g., 1700000000), while a milliseconds timestamp is 13 digits (e.g., 1700000000000). JavaScript Date.now() returns milliseconds, while most Unix systems use seconds. This tool detects and handles both formats.

No. Unix timestamps do not include leap seconds, they represent the number of non-leap seconds since January 1, 1970 UTC. This is consistent with how all major operating systems and programming languages handle Unix time.

Yes. The tool supports conversion across multiple timezones. You can select your target timezone from the available options to see the corresponding local date and time for any Unix timestamp.

The tool uses JavaScript Date objects, which can represent dates from April 20, 271,821 BCE to September 13, 275,760 CE. In practice, timestamps beyond the year 2038 (the 32-bit Unix timestamp limit) work fine here because JavaScript uses 64-bit floating point numbers.

Yes. The converter uses the browser's native Intl API with IANA timezone identifiers (e.g., "America/New_York" instead of "EST"), which automatically applies the correct DST offset for the specific date and time you entered. A date in July will use EDT (UTC-4), while the same city in January will use EST (UTC-5). This makes the tool accurate across DST transitions without any manual adjustment.

A UTC offset (like UTC+3) is a fixed number of hours ahead of or behind UTC. A timezone (like "Europe/Istanbul") is a named region that may change its UTC offset throughout the year due to Daylight Saving Time. UTC+3 is always 3 hours ahead of UTC, but Europe/Istanbul is UTC+3 in winter and UTC+3 year-round (Turkey stopped DST in 2016). Always use IANA timezone names for scheduling to avoid DST bugs.

DST transitions happen on different dates in different countries. The US "springs forward" on the second Sunday in March, while Europe changes on the last Sunday in March. During the gap between these dates, the time difference between US and European cities changes by one hour. When scheduling recurring meetings across DST boundaries, always confirm in both parties' local times. Using UTC for scheduling and converting to local time at display avoids DST confusion entirely.

Select the city from the source or target timezone list, enter the current date and time, and look at the result row for that city. The time zone abbreviation shown (e.g., EST, CEST, JST) indicates the current offset. Alternatively, the UTC row always shows the source time converted to UTC, which lets you calculate the offset manually.

IST is ambiguous and can mean Indian Standard Time (UTC+5:30), Irish Standard Time (UTC+1, summer only), or Israeli Standard Time (UTC+2, summer only). This is why IANA timezone identifiers like "Asia/Kolkata" for India and "Europe/Dublin" for Ireland are unambiguous. Always use IANA names in code, abbreviations like IST, CST, and EST are not standardized and can mean different things in different regions.

Store all timestamps in UTC. When writing to the database, convert user local time to UTC first. When reading, convert from UTC to the user's local timezone for display. Storing in UTC means the stored value is unambiguous regardless of DST changes or the user's location. Use the Unix timestamp (seconds or milliseconds since epoch) or an ISO 8601 string with a Z suffix (e.g., 2024-01-15T14:30:00Z) for maximum portability across systems and languages.

Systems storing Unix time in a signed 32-bit integer overflow on 19 January 2038 at 03:14:07 UTC, wrapping to December 1901. Modern 64-bit systems and databases are unaffected, but embedded devices, old file formats, and legacy protocols still carry the risk, it's the reason new designs should always store timestamps in 64 bits.

RFC 3339 is the strict internet profile of ISO 8601: it requires a complete date-time with numeric UTC offset (2026-06-12T14:30:00+03:00 or ...Z), while ISO 8601 also permits week dates, ordinal dates, and reduced precision. For APIs, target RFC 3339, anything that parses it also parses the common ISO forms.

Anchor the meeting to ONE person's named timezone (IANA, e.g. 'America/New_York'), not to a fixed UTC time, and let everyone else convert from there. Here's the subtlety: for HUMAN events like a 9am standup, you want it to stay 9am local for the anchor city even across DST, so storing it as a fixed UTC time is actually WRONG, because the UTC time would shift the local time by an hour when DST changes. Calendar apps handle this correctly when you set a timezone on the event. The catch is that participants in OTHER countries will see the meeting move by an hour during the weeks when their region and the anchor region are on different DST schedules, that's unavoidable and expected, so confirm the converted time around DST transition dates (mid-March and late-March differ between the US and Europe).

A handful of regions chose offsets that aren't round hours, usually for historical or solar-noon-alignment reasons. India is UTC+5:30, Iran is +3:30, and Nepal is famously +5:45, a 45-minute offset shared by almost nowhere else. Parts of Australia (+9:30, +10:30) and Newfoundland (−3:30) also use half-hour offsets. This is exactly why you should never assume timezones are whole-hour shifts in code, and why you must use a real timezone library/IANA database rather than naive arithmetic, adding '5 hours' for India would put you 30 minutes off, breaking timestamps and schedules.