Whether you’re building a booking system, calculating age, or managing payment terms, you’ll need reliable methods to find the number of days between dates.

In this comprehensive guide, you’ll discover seven battle-tested approaches to calculate date differences in Java, complete with practical examples and performance insights that will help you choose the right method for your specific use case.

1. Using Java 8+ Modern Date-Time API

A. ChronoUnit.DAYS.between()

ChronoUnit.DAYS.between() is one of the most straightforward methods you can use to calculate days between dates in Java 8+.

You can easily find the exact number of days between two LocalDate objects, and the method automatically handles leap years and date normalization.

Here’s a simple example: 

LocalDate startDate = LocalDate.of(2023, 1, 1); 
LocalDate endDate = LocalDate.of(2023, 12, 31); 
long daysBetween = ChronoUnit.DAYS.between(startDate, endDate); 
System.out.println("Days between dates: " + daysBetween); // 364

B. Period.between() Method

Using Period.between() gives you more detailed information about the time difference, including years, months, and days.

Here’s how you can implement it: 

LocalDate date1 = LocalDate.of(2023, 1, 1); 
LocalDate date2 = LocalDate.of(2024, 2, 15); 
Period period = Period.between(date1, date2); 
// Gets days part only
System.out.println("Days: " + period.getDays());

Plus, you should know that Period.between() provides additional flexibility when you need to work with different time units.

The method returns a Period object that lets you extract years, months, and days separately, making it perfect for scenarios where you need to display time differences in a human-readable format.

C. LocalDate.until() Approach

LocalDate.until() offers similar functionality to Period.between(), but with a more intuitive API.

You can specify the desired time unit directly in the method call: 

LocalDate start = LocalDate.of(2023, 1, 1); 
LocalDate end = LocalDate.of(2023, 12, 31); 
long days = start.until(end, ChronoUnit.DAYS); 
System.out.println("Days until: " + days); // Output: 364

Understanding the LocalDate.until() method helps you handle various time-based calculations more effectively.

You can use it with different ChronoUnits (DAYS, MONTHS, YEARS) and even chain it with other date-time operations.

This flexibility makes it particularly useful when building date-related features in your applications.

2. Legacy Date API Solutions

Let’s examine the legacy Date APIs.
While these methods are older, you might still encounter them in legacy code or need to maintain existing systems.

Understanding these approaches will help you work with older Java applications effectively.

A. Calendar Class Implementation

To calculate days between dates using java.util.Calendar class, you can utilize the getTimeInMillis() method.

Here’s a straightforward implementation: 

public static long getDaysDifference(Date startDate, Date endDate) { 
  Calendar startCal = Calendar.getInstance(); 
  startCal.setTime(startDate); 
  Calendar endCal = Calendar.getInstance(); 
  endCal.setTime(endDate); 
  long diff = endCal.getTimeInMillis() - 
                    startCal.getTimeInMillis(); 
  return TimeUnit.DAYS.convert(diff, TimeUnit.MILLISECONDS); 
}

B. Date Class Calculations

Practical implementation using the java.util.Date class involves converting both dates to milliseconds, finding their difference and converting those milliseconds to days by dividing with 24* 60 * 60 * 1000.
This is equivalent to number of milliseconds in 1 day.

Here’s how you can do it: 

public static long calculateDaysBetween(Date date1, Date date2) { 
  long difference = date2.getTime() - date1.getTime(); 
  return difference / (24 * 60 * 60 * 1000); 
}

Solutions using the Date class come with several considerations.

You need to handle time zones carefully, as the getTime() method returns milliseconds in UTC.

Additionally, you should account for daylight saving time changes which can affect your calculations.

While this method is simple, it’s less precise than modern alternatives due to potential rounding errors when dealing with milliseconds.

3. Using Third-Party Libraries

Despite Java’s built-in date handling capabilities, third-party libraries can offer more intuitive and feature-rich solutions for date calculations.

These libraries provide robust APIs that can simplify your date manipulation tasks while handling edge cases like leap years and time zones automatically.

A. Apache Commons DateUtils

For quick and reliable date difference calculations, Apache Commons DateUtils offers a straightforward approach.

Its DateUtils.daysBetween() method provides a clean way to calculate date differences without dealing with time zones or calendar complexities. 

import org.apache.commons.lang3.time.DateUtils; 
import java.util.Date; 

Date startDate = new Date(); 
Date endDate = // your end date 
long daysBetween = DateUtils.daysBetween(startDate, endDate);

B. Joda-Time Framework

One of the most popular date-time libraries, Joda-Time offers comprehensive date manipulation capabilities.

You can calculate date differences using Days.daysBetween() method, which handles time zones and calendar systems efficiently while providing clear, readable code. 

import org.joda.time.DateTime;
import org.joda.time.Days;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;

public class JodaDateDifferenceExample {
  public static void main(String[] args) {
    // Example 1: Calculate days between two dates using DateTime objects
    calculateDaysBetweenDates();

    // Example 2: Calculate days between dates from String
    calculateDaysBetweenDateStrings();
  }

  public static void calculateDaysBetweenDates() {
    // Create two DateTime objects
    // January 1, 2023
    DateTime startDate = new DateTime(2023, 1, 1, 0, 0); 
    // December 31, 2023
    DateTime endDate = new DateTime(2023, 12, 31, 0, 0); 

    // Calculate days between dates
    int daysBetween = Days.daysBetween(startDate, endDate).
                      getDays();
  }

  public static void calculateDaysBetweenDateStrings() {
    // Define date format
    DateTimeFormatter formatter = DateTimeFormat.
                                  forPattern("yyyy-MM-dd");

    // Parse date strings to DateTime objects
    String dateStr1 = "2023-01-01";
    String dateStr2 = "2023-12-31";

    DateTime date1 = formatter.parseDateTime(dateStr1);
    DateTime date2 = formatter.parseDateTime(dateStr2);

    // Calculate days between dates
    int daysBetween = Days.daysBetween(date1, date2).getDays();

    System.out.println("Days between " + dateStr1 + " and " +
                       dateStr2 + ": " + daysBetween);
  }
}

Solutions from Joda-Time are particularly useful when you need to handle complex date calculations.

The framework provides immutable date objects, ensuring thread safety in your applications.
You can work with different chronologies, perform date arithmetic, and format dates with minimal effort.

The library’s influence was so significant that it inspired many features in Java 8’s date-time API.

To wrap up

Summing up, you now have seven powerful methods to calculate date differences in Java, from modern LocalDate with ChronoUnit to legacy Calendar approaches and third-party solutions. Your choice depends on your specific needs.