EpochConverter/langs/Swift

Unix Timestamp in Swift

Swift uses Date and TimeInterval (a Double of seconds) for timestamps. On Apple platforms, CFAbsoluteTime is relative to Jan 1 2001 — always use Date.timeIntervalSince1970 for Unix epoch compatibility.

Code Examples

Current timestamp (seconds)

let seconds = Int(Date().timeIntervalSince1970)

timeIntervalSince1970 returns a Double (seconds with sub-second precision). Cast to Int for a whole-number Unix timestamp.

Current timestamp (milliseconds)

let milliseconds = Int(Date().timeIntervalSince1970 * 1000)

Multiply by 1000 before casting to Int. Useful when sending timestamps to JavaScript or Java APIs that expect milliseconds.

Convert timestamp to Date

let date = Date(timeIntervalSince1970: TimeInterval(timestamp))

Construct a Date from a Unix timestamp. Pass a Double or TimeInterval — if you have seconds as Int, cast it first.

Format Date as string

let fmt = ISO8601DateFormatter()
fmt.timeZone = TimeZone(identifier: "UTC")
let str = fmt.string(from: date)

ISO8601DateFormatter produces RFC 3339 / ISO 8601 output. Always set timeZone explicitly to avoid local-time surprises.

Using Foundation — formatted output

let formatted = Date(timeIntervalSince1970: Double(timestamp))
    .formatted(.dateTime.year().month().day().hour().minute().second().timeZone())

Swift 5.5+ formatted API. More expressive than DateFormatter for display strings, though not suitable for machine parsing.

Note

Swift's Date is a thin wrapper around a Double of seconds since January 1, 2001 (not 1970). Always use timeIntervalSince1970 when you need a Unix timestamp. CFAbsoluteTime and Date() internally differ by 978,307,200 seconds — a common source of bugs when mixing Core Foundation and Swift APIs.

Related Languages

Unix timestamp in Kotlin →Unix timestamp in JavaScript →Unix timestamp in Go →

Frequently Asked Questions

How do I get the current Unix timestamp in Swift?

Use Date().timeIntervalSince1970, which returns a Double representing seconds since January 1, 1970 UTC. Cast to Int for a whole-number Unix timestamp: let seconds = Int(Date().timeIntervalSince1970). No imports needed — Date is part of Foundation.

Why doesn't Swift's Date() directly give a Unix timestamp?

Swift's Date internally stores time as seconds since January 1, 2001 (Core Data epoch), not 1970. Always use .timeIntervalSince1970 to get Unix time. Using .timeIntervalSinceReferenceDate would give a value that's 978,307,200 seconds off — a common source of hard-to-spot bugs.

How do I get milliseconds in Swift?

Multiply timeIntervalSince1970 by 1000 before casting: let ms = Int(Date().timeIntervalSince1970 * 1000). This is needed when sending timestamps to JavaScript (Date.now()), Java (System.currentTimeMillis()), or any API that expects 13-digit millisecond timestamps.

How do I convert a Unix timestamp back to a Date in Swift?

Use Date(timeIntervalSince1970: TimeInterval(timestamp)). If you have an Int, cast it to Double first: Date(timeIntervalSince1970: Double(myIntTimestamp)). You can then format it with ISO8601DateFormatter or DateFormatter.

Should I use Int or Double for Unix timestamps in Swift?

Use Int for storing and transmitting timestamps — it's unambiguous and matches how most APIs and databases represent epoch seconds. Use Double (TimeInterval) for intermediate calculations involving sub-second precision, such as measuring durations or working with sub-second timestamps.

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