Kotlin Unix Timestamp Guide
Kotlin uses Java's java.time package for modern timestamp handling, with Kotlin-idiomatic syntax. Since Kotlin runs on the JVM, it has full access to Instant, LocalDateTime, and ZonedDateTime. Kotlin's concise syntax makes timestamp operations even cleaner than Java.
Unix timestamps are a universal way to represent a specific moment in time as a single integer, counting the seconds elapsed since January 1, 1970 (the Unix epoch). Working with timestamps in Kotlin is a common task for developers building applications that log events, schedule jobs, compare dates, or communicate with APIs. The examples below cover the three most essential operations: retrieving the current timestamp, converting a timestamp into a human-readable date, and converting a date back into a timestamp.
Get Current Timestamp
The most common starting point is to capture the current moment as a Unix timestamp. In Kotlin, you can obtain the number of seconds (or milliseconds) since the epoch using built-in functions. This value is useful for recording when an event occurred, setting cache expiry times, or generating time-based identifiers.
Get Current Unix Timestamp
import java.time.Instant
// Get current Unix timestamp
val timestamp = Instant.now().epochSecond
println(timestamp) // e.g., 1706745600
// With milliseconds
val timestampMs = System.currentTimeMillis()Convert Timestamp to Date
Once you have a Unix timestamp, you often need to display it in a human-readable format. Converting a raw integer like 1706745600 into a formatted date string such as "2024-02-01 00:00:00" makes it meaningful to end users. The following Kotlin code demonstrates how to perform this conversion with proper timezone handling.
Convert to Date
import java.time.*
// Convert Unix timestamp to date
val timestamp = 1706745600L
val instant = Instant.ofEpochSecond(timestamp)
val dt = LocalDateTime.ofInstant(instant, ZoneId.of("UTC"))
println(dt) // 2024-02-01T00:00Convert Date to Timestamp
The reverse operation is equally important. When users provide a date through a form or when your application reads dates from a file, you need to convert them into Unix timestamps for storage, comparison, or transmission via APIs. Here is how to convert a date or date string into a Unix timestamp in Kotlin.
Convert to Timestamp
import java.time.*
// Convert date to Unix timestamp
val dt = LocalDateTime.of(2024, 2, 1, 0, 0, 0)
val timestamp = dt.atZone(ZoneId.of("UTC")).toEpochSecond()
println(timestamp) // 1706745600Common Pitfalls in Kotlin
Working with timestamps can be error-prone, especially across different platforms and timezone configurations. Being aware of these common mistakes will help you write more robust Kotlin code and avoid subtle bugs that are difficult to trace in production.
- 1Kotlin Multiplatform doesn't have java.time — use kotlinx-datetime library instead
- 2System.currentTimeMillis() is JVM-only and returns milliseconds, not seconds
- 3LocalDateTime doesn't carry timezone info — specify ZoneId when converting to/from timestamps
- 4On Android API < 26, java.time requires desugaring or ThreeTenABP library
Best Practices for Timestamp Handling
Regardless of the programming language, following a few best practices will keep your timestamp code reliable. Always store and transmit timestamps in UTC to avoid timezone ambiguity. Use seconds-based Unix timestamps unless your application requires sub-second precision, in which case milliseconds or microseconds are appropriate. When displaying dates to users, convert from UTC to their local timezone only at the presentation layer. Document whether your APIs expect seconds or milliseconds, as mixing the two is one of the most frequent sources of timestamp bugs.
Frequently Asked Questions
Related Tools
Timestamp Guides for Other Languages
Need Unix timestamp examples for a different programming language? Browse our complete collection of language-specific guides with copy-paste code snippets.