Epoch Time Converter & Timezone Tool

What is Unix epoch time?

Unix epoch time (also called "Unix time" or a "timestamp") is the number of seconds that have elapsed since January 1, 1970, 00:00:00 UTC — the "epoch." It's a single, timezone-independent number, which is why databases, APIs, and server logs almost universally store timestamps this way instead of a formatted date string.

Worked examples

Epoch 0 is 1970-01-01T00:00:00 UTC, by definition. Epoch 1,000,000,000 — one billion seconds later — lands on 2001-09-09T01:46:40 UTC, a moment some engineers marked at the time as the "billennium." Both are useful sanity checks: if you convert a timestamp and land somewhere wildly outside the range you expected, the input was probably in the wrong unit or the wrong timezone was assumed.

For zone-to-zone conversion: 15:00 in New York during daylight saving time is UTC−4, so that's 19:00 UTC. Kolkata is UTC+5:30 year-round (India doesn't observe DST), so add 5 hours 30 minutes: 00:30 the next day in Kolkata. Two things trip people up in that single conversion: the offset isn't a whole number of hours, and the date itself rolls over — 3 PM in New York is already past midnight the following day in India. A converter that only shows the time and not the date will silently give you the wrong day.

Seconds vs. milliseconds — the 1000× mistake

Unix epoch time is defined in seconds, but JavaScript's Date.now() and many web APIs return epoch milliseconds instead. The fields on this page expect seconds. As a rule of thumb, current epoch seconds is a 10-digit number; current epoch milliseconds is 13 digits. Pasting a 13-digit millisecond value into a seconds field doesn't error — it just computes a date roughly 1,000× further in the future, landing thousands of years out. If a "seconds" timestamp you're converting resolves to a date decades or centuries away from what you expected, check whether the source actually gave you milliseconds.

Common mistakes

• Treating an abbreviation as unambiguous. IST alone could mean India, Ireland, or Israel Standard Time; CST could mean US Central, China, or Cuba. This tool's zone search shows the country alongside every match so you can tell them apart — always confirm the country, not just the three letters.
• Assuming a US zone has one fixed UTC offset. "Eastern Time" is UTC−5 in winter (EST) and UTC−4 in summer (EDT) — a full hour of difference depending on the date. Hardcoding "Eastern = UTC−5" is a common source of off-by-one-hour bugs for roughly eight months of the year.
• Forgetting the date can shift. As shown in the New York → Kolkata example above, a large positive offset can push the result into the next calendar day, and a large negative one can push it into the previous day. Always check the date, not just the clock time.

DST correctness and the March-forward gap

Twice a year, clocks in DST-observing regions either skip an hour forward or fold an hour back. Converting a wall-clock time to an absolute instant correctly requires a two-pass resolution: compute the zone's offset for the requested date, apply it, then recompute the offset at the resulting instant and adjust if it changed — a naive single-pass calculation can be an hour wrong right around a transition. On March 8, 2026, clocks in most of the US spring forward at 2:00 AM directly to 3:00 AM, so the wall-clock time 2:30 AM that day simply doesn't exist in that zone. This tool detects that case and shows a warning instead of silently returning a wrong or misleading answer.

Why not just use a date string?

A raw number is unambiguous and easy to compare, sort, or do arithmetic on — no parsing, no locale formatting issues, and no ambiguity about which timezone was intended. It only becomes a human-readable date at the moment it's displayed, which is exactly what this converter does in both directions.

When not to use it

This tool converts a single point in time correctly for today's timezone rules — it isn't a substitute for a calendar/scheduling tool when you need a recurring meeting to land at the same local time every week. A weekly call scheduled from a US zone to an Indian one will appear to shift by an hour, twice a year, whenever only one of the two countries changes its clocks — each occurrence needs to be checked individually, which is what dedicated calendar software (not a one-off converter) is built to handle. It also isn't built for historical dates before a region's currently-known timezone rules took effect; political changes to a country's offset or DST policy are only as accurate as the underlying browser's timezone database.

World clock

The pinned-zones list below the converter keeps a running clock for the zones you use most, saved to this device, useful for a quick glance without re-running a conversion.