Increment a date and calculate whether two dates differ.

← Date, Time, and Duration · Ref: Q1173

++ advances Date by one day, <=> compares:

  today++
  cmp <- today <=> targetDate

-- goes backward. DateTime increments by one second instead. See Q1103.

Example

defines module qa.datetimeduration.datearithmetic

  defines program

    DateArithmeticDemo()
      stdout <- Stdout()

      today <- 2026-04-07
      stdout.println(`Today: ${today}`)

      //Increment by one day
      today++
      stdout.println(`Tomorrow: ${today}`)

      //Compare dates
      targetDate <- 2026-04-09
      cmp <- today <=> targetDate
      stdout.println(`Comparison: ${cmp}`)

Common mistakes

E50060 — EK9 Date has no plusDays() method — use ++ to advance a Date by one day. See ek9 -h E50060 for details.

Incorrect:

      today.plusDays(1)

Correct:

      today++

Other ways to ask this

I need to advance a date by one day using the ++ operator
In Java I'd use LocalDate.plusDays(1). Write the EK9 date increment
Given a date, step forward one day and compare with another date
Move a date forward using ++ and check equality with ==

Coming from another language?

Java: date.plusDays(1). Python: date + timedelta(days=1). Rust: date + Duration::days(1). EK9: date++ (one day forward).

Keywords: compare, day, arithmetic, ++, increment, date