Calendar cal = Calendar.getInstance();
cal.setTime(new Date());
cal.add(Calendar.MONTH, -3);

Set your date using setTime method.

Using Java 8 you can do it like this,

Date d = Date.from(LocalDate.now().minusMonths(3).atStartOfDay(ZoneId.systemDefault()).toInstant());

The LocalDate class has a lot of methods to help you make easy computations about dates like the above,

// Add 2 months
Date d = Date.from(LocalDate.now().plusMonths(2).atStartOfDay(ZoneId.systemDefault()).toInstant());
// Add 5 days
Date d = Date.from(LocalDate.now().plusDays(5).atStartOfDay(ZoneId.systemDefault()).toInstant());
// Minus 1 day and 1 year
Date d = Date.from(LocalDate.now().minusYears(1).minusDays(1).atStartOfDay(ZoneId.systemDefault()).toInstant());

In order to compute time you can use the LocalDateTime class,

// Minus 1 year, minus 1 days, plus 1 hour
Date d = Date.from(LocalDateTime.now().minusYears(1).minusDays(1).plusHours(1).toLocalDate().atStartOfDay(ZoneId.systemDefault()).toInstant());

I always recommend Joda for this sort of stuff. It has a much nicer API, and doesn't suffer from threading issues that the standard Java date/time has (e.g. issues with SimpleDateFormat, or general mutability).

e.g.

DateTime result = dt.minusMonths(3);

Ok with java.sql.Date (subclass of java.util.Date) and JDK's 8 LocalDate help you can do it in one line ;)

Date date = java.sql.Date.valueOf(LocalDate.now().minus(3, ChronoUnit.MONTHS));

The Date class itself isn't enough (+: You've got to use the Calendar class here

Something along these lines

GregorianCalendar lCalendar = new GregorianCalendar();
lCalendar.setTime( aDate );
lCalendar.add(Calendar.MONTH, -3);

p.s. the snippet above is not tested to be compilable.

You want today - 3 Month formatted as dd MMMM yyyy

     SimpleDateFormat format = new SimpleDateFormat("dd MMMM yyyy");

     Calendar c = Calendar.getInstance(); 
     c.setTime(new Date()); 
     c.add(Calendar.MONTH, -3);

     Date d = c.getTime();
     String res = format.format(d);

     System.out.println(res);

So this code can do the job ;)

public static Date getDateMonthsAgo(int numOfMonthsAgo)
{
    Calendar c = Calendar.getInstance(); 
    c.setTime(new Date()); 
    c.add(Calendar.MONTH, -1 * numOfMonthsAgo);
    return c.getTime();
}

will return the date X months in the past. Similarily, here's a function that returns the date X days in the past.

public static Date getDateDaysAgo(int numOfDaysAgo)
{
    Calendar c = Calendar.getInstance(); 
    c.setTime(new Date()); 
    c.add(Calendar.DAY_OF_YEAR, -1 * numOfDaysAgo);
    return c.getTime();
}

You can use Apache Commons Lang3 DateUtils addMonths function.

static Date addMonths(Date date, int amount)

Adds a number of months to a date returning a new object. The original Date is unchanged. The amount to add, may be negative, so you can go 3 months back.

You can use

Date d1 = new Date()
d1.setMonth(d1.month-3)

Hope this helps

String startDate="15/10/1987";

    Date date = new SimpleDateFormat("dd/MM/yyyy").parse(startDate);
    String formattedDate = new SimpleDateFormat("yyyy-MM-dd").format(date);
    LocalDate today = LocalDate.parse(formattedDate);
    String endDate=today.minusMonths(3).toString();