Cookbooks
Kotlin
Chapter 7. Dates and Times
Calculating a date in the future or past

Kotlin:
Calculating a date in the future or past

How to:

Kotlin handles dates and times with the java.time library. To add or subtract days, use plusDays() or minusDays(). Here’s the skinny:

import java.time.LocalDate

fun main() {
    val today = LocalDate.now()
    val tenDaysLater = today.plusDays(10)
    val tenDaysBefore = today.minusDays(10)
    
    println("Today: $today")
    println("Ten days from now: $tenDaysLater")
    println("Ten days ago: $tenDaysBefore")
}

Sample output:

Today: 2023-03-15
Ten days from now: 2023-03-25
Ten days ago: 2023-03-05

Beyond days, you can also play with months and years (plusMonths(), minusMonths(), plusYears(), minusYears()).

Deep Dive

Calculating dates isn’t new. Since Java 8, the java.time package has been the go-to for date-time arithmetic—much better than old Calendar or Date, which were clunky and not thread-safe.

java.time uses immutable objects, so you avoid nasty bugs from accidentally modifying your dates. Objects like LocalDate, LocalTime, LocalDateTime, and ZonedDateTime help you represent different aspects of time precisely.

Alternatives? Of course. Before java.time, Joda-Time was the weapon of choice. Some older systems still use it. And in the Android realm, the ThreeTenABP library backports java.time features for compatibility with Java 6 & 7 circumstances.

The java.time API is also designed to be timezone-aware, thanks to classes like ZonedDateTime. So when you’re shimmying dates around, you can respect the chronology of Earth’s spin.

See Also

Comparing two dates