For a Unix timestamp in seconds, multiply by 1,000 before passing it to JavaScript’s Date constructor: new Date(unixSeconds * 1000). JavaScript date values use milliseconds, so passing seconds directly usually produces a date near the start of 1970.
Convert Unix seconds to a JavaScript Date
A common Unix timestamp counts seconds since 1970-01-01 00:00:00 UTC. JavaScript’s numeric Date time value counts milliseconds from that epoch. Multiply seconds by 1,000 to convert the unit:
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const unixSeconds = 1_700_000_000;
const date = new Date(unixSeconds * 1000);
console.log(date.toISOString());
// 2023-11-14T22:13:20.000ZThe multiplication changes seconds into milliseconds; it does not convert the instant to another time zone. A JavaScript Date represents an instant. The method used to display it determines the time-zone presentation. MDN explains the millisecond representation in its guide to representing dates and times.
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Do not multiply a timestamp that is already in milliseconds. Apply the conversion at the point the value enters your application, based on the source’s contract rather than an unexplained guess about its size.
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- Seconds:
new Date(timestamp * 1000) - Milliseconds:
new Date(timestamp)
const seconds = 1_700_000_000;
const milliseconds = 1_700_000_000_000;
const fromSeconds = new Date(seconds * 1000);
const fromMilliseconds = new Date(milliseconds);The constructor matters: use new Date(value) to create a date from a numeric timestamp. Calling Date(value) without new returns the current date-time as a string and ignores the supplied argument. See MDN’s Date() constructor reference.
Choose the right output and time zone
Use the output method that matches the consumer. For stable, machine-readable UTC text, call toISOString(); its result ends in Z. For people, use toLocaleString(). If the display must follow a particular region’s time-zone rules, pass an explicit IANA time-zone identifier rather than relying on the computer’s configured zone.
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| Need | Use | Time-zone behavior |
|---|---|---|
| Standard UTC string for data exchange | date.toISOString() |
UTC; ends in Z |
| Display in the runtime’s local zone | date.toString() |
Uses the host’s local time zone |
| Localized display in a chosen region | date.toLocaleString("en-US", { timeZone: "America/Los_Angeles" }) |
Uses the specified zone’s rules |
const date = new Date(unixSeconds * 1000);
const utcText = date.toISOString();
const localText = date.toLocaleString("en-US", {
timeZone: "America/Los_Angeles",
});Local display can show a different clock time or calendar date from UTC, depending on the zone. For details, see MDN’s references for toISOString() and toString().
Validate the timestamp and handle edge cases
A numeric value outside JavaScript’s supported Date range, or a value that cannot produce a valid date, results in an invalid Date. The supported range is ±8,640,000,000,000,000 milliseconds from the epoch. Check the resulting time value with Number.isNaN(date.getTime()) before using it:
function dateFromUnixSeconds(unixSeconds) {
const date = new Date(unixSeconds * 1000);
if (Number.isNaN(date.getTime())) {
throw new RangeError("Timestamp is outside the supported Date range");
}
return date;
}Negative timestamps are valid when they fall within the supported range; they represent instants before 1970-01-01 UTC. Fractional seconds may also be supplied. If a source system specifies how fractional values must be rounded or truncated, follow that contract; do not silently impose a rounding rule of your own. MDN documents the constructor’s supported range and invalid-date behavior.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why does my JavaScript date show 1970?
The usual cause is passing a seconds-based Unix timestamp directly to new Date(). The constructor interprets a number as milliseconds, so a seconds value is treated as a much smaller interval after the epoch. If the input is in seconds, use new Date(timestamp * 1000); if it is already in milliseconds, pass it directly. Numeric timestamps can be converted without Date.parse() or an intermediate date string.
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