# Unix timestamp converter

> Unix timestamp converter: epoch seconds, milliseconds, microseconds or nanoseconds to an ISO 8601 UTC date and local time, and dates back to epoch time.

Interactive version: https://www.calcopenly.com/datetime/unix-timestamp-converter
Subject: Date and time calculators

A Unix timestamp counts the seconds since 00:00:00 UTC on 1 January 1970, the Unix epoch, with every day counted as exactly 86,400 seconds. The converter splits the count into whole days and seconds of the day, turns the day number into a calendar date, then applies the chosen zone's offset from the IANA time zone database. Date to timestamp runs the same steps backwards.

Developers use it to read log lines, database columns and API fields. With the unit left on automatic, up to 11 digits are read as seconds, 12 to 14 as milliseconds, 15 to 17 as microseconds and 18 or more as nanoseconds, so 1700000000000 is read as milliseconds: 22:13:20 UTC on 14 November 2023.

Results cover the years 0001 to 9999, the range of a four-digit ISO 8601 year. Negative timestamps are instants before 1970; −86400 is midnight UTC on 31 December 1969.

## Inputs

- **Convert** (options: Timestamp to date, Date to timestamp)
- **Timestamp**: Digits (optionally negative or with a decimal part), an ISO 8601 date-time such as 2026-01-15T09:00:00Z, or “now”.
- **Timestamp unit** (options: Detect from length, Seconds, Milliseconds, Microseconds, Nanoseconds)
- **Date**
- **Time**
- **Time zone** (options: This device's time zone, UTC, Honolulu, Anchorage, Los Angeles, Denver, Phoenix, Chicago, Mexico City, New York, Toronto, Bogotá, Halifax, St John's, Santiago, São Paulo, Buenos Aires, Reykjavík, London, Dublin, Lisbon, Lagos, Casablanca, Paris, Berlin, Madrid, Rome, Amsterdam, Stockholm, Oslo, Johannesburg, Cairo, Athens, Helsinki, Kyiv, Istanbul, Nairobi, Moscow, Riyadh, Tehran, Dubai, Karachi, India (Kolkata), Kathmandu, Dhaka, Bangkok, Jakarta, Singapore, China (Shanghai), Hong Kong, Manila, Perth, Seoul, Tokyo, Adelaide, Brisbane, Sydney, Auckland, Chatham Islands, Kiritimati)
- **If the time happens twice (clocks going back)** (options: Use the first occurrence, Use the second occurrence)

## Results

- ISO 8601 (UTC) — main result
- Local time in the chosen zone
- Unix seconds
- Milliseconds
- Microseconds
- Nanoseconds
- Day of the week (UTC)
- Read as
- Relative to now

## Formula

$$
t = 86400 \times N(\text{date}) + 3600h + 60m + s,\qquad N = \text{days since 1970-01-01}
$$

## Worked examples

### The epoch

- Convert: Timestamp to date
- Timestamp: 0
- Timestamp unit: Seconds
- Time zone: UTC
- **ISO 8601 (UTC): 1970-01-01T00:00:00Z**
- **Day of the week (UTC): Thursday**
- Checked against: POSIX definition; Python datetime.fromtimestamp(0, timezone.utc)

### Largest signed 32-bit value (year 2038)

- Convert: Timestamp to date
- Timestamp: 2147483647
- Timestamp unit: Detect from length
- Time zone: UTC
- **ISO 8601 (UTC): 2038-01-19T03:14:07Z**
- **Read as: seconds**
- Checked against: Python 3.8: datetime.fromtimestamp(2147483647, timezone.utc)

### Milliseconds shown in India

- Convert: Timestamp to date
- Timestamp: 1700000000000
- Timestamp unit: Detect from length
- Time zone: India (Kolkata)
- **ISO 8601 (UTC): 2023-11-14T22:13:20Z**
- **Local time in the chosen zone: 2023-11-15 03:43:20 (UTC+05:30)**
- **Unix seconds: 1700000000**
- **Read as: milliseconds**
- Checked against: Python 3.8: datetime.fromtimestamp(1700000000, tz=Asia/Kolkata) = 2023-11-15 03:43:20+05:30

### Negative timestamp

- Convert: Timestamp to date
- Timestamp: -86400
- Timestamp unit: Seconds
- Time zone: UTC
- **ISO 8601 (UTC): 1969-12-31T00:00:00Z**
- **Day of the week (UTC): Wednesday**
- Checked against: Python 3.8: datetime.fromtimestamp(-86400, timezone.utc)

### Nanoseconds keep every digit

- Convert: Timestamp to date
- Timestamp: 1768478400123456789
- Timestamp unit: Detect from length
- Time zone: UTC
- **ISO 8601 (UTC): 2026-01-15T12:00:00.123456789Z**
- **Milliseconds: 1768478400123.456789**
- **Read as: nanoseconds**
- Checked against: Python 3.8: datetime.fromtimestamp(1768478400, timezone.utc) = 2026-01-15T12:00:00Z; fraction .123456789 s by definition

### ISO 8601 with an offset, on a leap day

- Convert: Timestamp to date
- Timestamp: 2024-02-29T12:34:56.789+05:30
- Timestamp unit: Detect from length
- Time zone: UTC
- **Unix seconds: 1709190296.789**
- **ISO 8601 (UTC): 2024-02-29T07:04:56.789Z**
- **Read as: ISO 8601 with offset**
- Checked against: Python 3.8: datetime.fromisoformat('2024-02-29T12:34:56.789+05:30').timestamp() = 1709190296.789

## Questions

### What is the year 2038 problem?

Software that stores Unix time in a signed 32-bit integer can count only to 2,147,483,647 seconds, reached at 03:14:07 UTC on 19 January 2038. One second later the value wraps to −2,147,483,648, which reads as 20:45:52 UTC on 13 December 1901. A signed 64-bit count, the usual size on current 64-bit systems, lasts about 292 billion years.

### How can I tell whether a timestamp is in seconds or milliseconds?

Count the digits. Present-day times have 10 digits in seconds, 13 in milliseconds, 16 in microseconds and 19 in nanoseconds; the seconds count reached 1,000,000,000 on 9 September 2001 and stays at 10 digits until 20 November 2286. JavaScript's Date.now() and Java's System.currentTimeMillis() return milliseconds, while the shell command date +%s and Python's time.time() return seconds.

### Does Unix time count leap seconds?

No. POSIX defines every day as 86,400 seconds, so the 27 leap seconds added to UTC between 1972 and 2016 have no timestamps of their own, and 23:59:60 cannot be written as Unix time. Systems either repeat a second when one occurs or spread it out; Google, for example, smears a leap second over the 24 hours from noon to noon UTC.

### Is a Unix timestamp the same in every time zone?

Yes. A timestamp names one instant, and the zone only changes how that instant is written. Timestamp 0 is 00:00 UTC on 1 January 1970, which was 05:30 the same day in India, 19:00 on 31 December 1969 in New York, and 01:00 in London, where British Standard Time kept clocks on UTC+01:00 all year from 1968 to 1971.

### How do I get the current Unix timestamp?

Type now in the timestamp box, or ask the system clock: date +%s in a Linux or macOS shell, Math.floor(Date.now() / 1000) in JavaScript, int(time.time()) in Python, and SELECT UNIX_TIMESTAMP() in MySQL. The count grows by 86,400 a day and passes 1,800,000,000 at 08:00 UTC on 15 January 2027.

### How accurate is the Unix timestamp converter?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 8 worked examples whose answers come from independent sources; for example, “The epoch” is checked against POSIX definition; Python datetime.fromtimestamp(0, timezone.utc).

### Where does the method come from?

POSIX.1-2017, §4.16 Seconds Since the Epoch; ISO 8601-1:2019 — Date and time representations; IANA Time Zone Database.

## Sources

- [POSIX.1-2017, §4.16 Seconds Since the Epoch](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_16)
- ISO 8601-1:2019 — Date and time representations
- [IANA Time Zone Database](https://www.iana.org/time-zones)