How to Work with Dates and Time in Kotlin with the Java Time API

REIT monero

2 min read

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Jun 4, 2025

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Working with dates and time can quickly become a headache in any programming language. Fortunately, Kotlin leverages the robust Java Time API introduced in Java 8, which offers a clean, immutable, and powerful approach to date and time manipulation. Whether you’re building scheduling features, formatting timestamps, or performing date arithmetic, the Java Time API gives you all the tools you need.

🕒 Getting Started with java.time

The java.time package offers several key classes:

• LocalDate – A date without time (e.g., 2025-06-04)
• LocalTime – A time without date (e.g., 14:35:20)
• LocalDateTime – Date and time without a timezone
• ZonedDateTime – Date and time with a timezone
• Instant – A point on the timeline (in UTC)

These classes are immutable and thread-safe, making them perfect for multi-threaded applications.

📅 Creating Date and Time Instances

Using now():

import java.time.*

val currentDate = LocalDate.now()
val currentTime = LocalTime.now()
val currentDateTime = LocalDateTime.now()
val currentInstant = Instant.now()println("Date: $currentDate")
println("Time: $currentTime")
println("DateTime: $currentDateTime")
println("Instant: $currentInstant")

Using of():

val customDate = LocalDate.of(2025, Month.JUNE, 4)
val customTime = LocalTime.of(14, 30)
val customDateTime = LocalDateTime.of(customDate, customTime)

🛠 Manipulating Dates and Time

You can easily perform operations like adding or subtracting days, months, or years.

val nextWeek = currentDate.plusWeeks(1)
val lastMonth = currentDate.minusMonths(1)
val tomorrow = currentDate.plusDays(1)

Want to know the day of the week?

val dayOfWeek = currentDate.dayOfWeek
println("Today is: $dayOfWeek")

🕹 Formatting and Parsing

Formatting and parsing are done using DateTimeFormatter.

Formatting:

import java.time.format.DateTimeFormatter

val formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm")
val formatted = currentDateTime.format(formatter)println("Formatted datetime: $formatted")

Parsing:

val dateString = "04-06-2025 14:30"
val parsedDateTime = LocalDateTime.parse(dateString, formatter)
println("Parsed datetime: $parsedDateTime")

🌍 Working with Time Zones

If you’re dealing with global users, use ZonedDateTime.

val zonedDateTime = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"))
println("Tokyo time: $zonedDateTime")

val utc = ZonedDateTime.now(ZoneOffset.UTC)
println("UTC time: $utc")

Convert between zones:

val newYorkTime = zonedDateTime.withZoneSameInstant(ZoneId.of("America/New_York"))
println("New York time: $newYorkTime")

⏳ Calculating Duration and Period

Duration – for time-based differences (hours, minutes, seconds):

val startTime = LocalTime.of(9, 0)
val endTime = LocalTime.of(17, 30)

val duration = Duration.between(startTime, endTime)
println("Duration in hours: ${duration.toHours()}")

Period – for date-based differences (days, months, years):

val startDate = LocalDate.of(2020, 1, 1)
val endDate = LocalDate.of(2025, 6, 4)

val period = Period.between(startDate, endDate)
println("Period: ${period.years} years, ${period.months} months, ${period.days} days")

🔁 Convert Between Legacy Date and Java Time

Need to work with legacy java.util.Date?

import java.util.Date
import java.time.ZoneId

val date = Date()
val instantFromDate = date.toInstant()
val localDateTime = LocalDateTime.ofInstant(instantFromDate, ZoneId.systemDefault())// Reverse
val dateFromInstant = Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant())

Final Thoughts

Kotlin’s seamless interop with the Java Time API makes working with date and time intuitive, safe, and powerful. You avoid mutable classes like Calendar and the error-prone Date class while benefiting from immutability and clear APIs.

Pro Tip: Always prefer ZonedDateTime or Instant when storing dates that will be used across different time zones. It helps prevent many localization and daylight saving bugs.