Convert Unix timestamps to human-readable dates and back with millisecond precision.
Every Unix timestamp is a plain count of seconds since 1970-01-01 00:00:00 UTC, and the count itself carries no timezone. Paste one into this tool and it resolves to a calendar date and clock time, shown in UTC and in your local zone; type a date and it returns the count. Millisecond values, 13 digits instead of 10, are handled without a separate step. The first mistake most users make is scale: read a millisecond value as seconds and the date lands tens of thousands of years in the future, while the reverse lands in January 1970.
A concrete input and expected output from the current implementation.
Input
1755367200
Expected output
2025-08-16 18:00:00 UTC (also written 1755367200000 in milliseconds)
Dividing 1,755,367,200 by 86,400 gives 20,316.75: 20,316 full days plus 0.75 of a day. Counting 20,316 days from 1970-01-01 reaches 2025-08-16, and 0.75 day is 18 hours, so the instant is 18:00 UTC. The millisecond form is the same digits with three zeros appended.
A 10-digit value is treated as seconds and a 13-digit value as milliseconds, divided by 1,000 before counting; each day counts as exactly 86,400 seconds in UTC. The reverse direction parses the entered date and time, then counts the seconds back to the epoch. Leap seconds are absorbed rather than added, so Unix time always ticks in whole 86,400-second days.
The timestamp names one instant and no zone; the tool renders it in UTC and in the browser's local zone side by side, so the local column legitimately differs between viewers. When converting a date back to a number, an entered time without a zone is counted as UTC, because a timestamp can only represent one instant. If you meant local time, subtract your offset before converting.
Because a Unix timestamp names one instant, and each person's browser renders that instant in its own zone. The number 1755367200 is exactly 2025-08-16 18:00:00 UTC for everyone; someone in Tokyo sees 03:00 the next day, someone in New York sees 14:00. Nothing is wrong - compare UTC values, not local strings.
Count digits and scale. Values around 1.7 to 1.8 billion (10 digits) are seconds and date to the present era; values around 1.7 to 1.8 trillion (13 digits) are milliseconds. Divide the 13-digit number by 1,000 to get the seconds form. A 10-digit value near 1.7 billion read as milliseconds would date to January 1970.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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