Calculate Age in Java

1. Overview

In this quick tutorial, we’ll see how to calculate age using Java 8, Java 7 and Joda-Time libraries.

In all cases, we’ll take the birth date and current date as input and return the calculated age in years.

2. Using Java 8

Java 8 introduced a new Date-Time API for working with dates and times, largely based off of the Joda-Time library.

In Java 8, we can use java.time.LocalDate for our birth date and current date, and then use Period to calculate their difference in years:

public int calculateAge(
  LocalDate birthDate,
  LocalDate currentDate) {
    // validate inputs ...
    return Period.between(birthDate, currentDate).getYears();
}

LocalDate is helpful here because represents just a date, compared to Java’s Date class, which represents both a date and a time. LocalDate.now() can give us the current date.

And Period is helpful when we need to think about time periods in years, months and days.

If we wanted to get a more exact age, say in seconds, then we’d want to take a look at LocalDateTime and Duration, respectively (and maybe return a long instead).

3. Using Joda-Time

If Java 8 isn’t an option, we can still get the same kind of result from Joda-Time, a de-facto standard for date-time operations in the pre-Java 8 world.

We need to add the Joda-Time dependency to our pom:

<dependency>
  <groupId>joda-time</groupId>
  <artifactId>joda-time</artifactId>
  <version>2.10</version>
</dependency>

And then we can write a similar method to calculate age, this time using LocalDate and Years from Joda-Time:

public int calculateAgeWithJodaTime(
  org.joda.time.LocalDate birthDate,
  org.joda.time.LocalDate currentDate) {
    // validate inputs ...
    Years age = Years.yearsBetween(birthDate, currentDate);
    return age.getYears();   
}

4. Using Java 7

Without a dedicated API in Java 7, we are left to roll our own, and so there are quite a few approaches.

As one example, we can use java.util.Date:

public int calculateAgeWithJava7(
  Date birthDate, 
  Date currentDate) {            
    // validate inputs ...                                                                               
    DateFormat formatter = new SimpleDateFormat("yyyyMMdd");                           
    int d1 = Integer.parseInt(formatter.format(birthDate));                            
    int d2 = Integer.parseInt(formatter.format(currentDate));                          
    int age = (d2 - d1) / 10000;                                                       
    return age;                                                                        
}

Here, we convert the given birthDate and currentDate objects into integers and find the difference between them, and so long as we aren’t still on Java 7 in 8000 years, this approach should work until then.

5. Conclusion

In this article, we showed out how to calculate age easily using Java 8, Java 7 and Joda-Time libraries.

To learn more about Java 8’s data-time support check out our Java 8 date-time intro.

And as always, the complete code for these snippets can be found over on GitHub.