Question

For instance, the actual age it should return is 47… using this code it returns me 48. Am i doing the right way of applying the logic and calculating the age in days, months and year.

Answer 1

Assumption that 12 months times 30 days is a year – that’s what’s most wrong in here (that’s 360 days, while in fact 1 year is close to 365.25 days on average).

What you should be doing, is calculating each segment separately:

var now = new Date();
var years = now.getFullYear()-formattedDate.getFullYear();
var months = now.getMonth()-formattedDate.getMonth();
var days = now.getDate()-formattedDate.getDate();

if (months < 0) {
    months += 12;
    years -= 1;
}

if (days < 0) {
    months -= 1;
    // now days here is a little trickier - we need the number of days in last month
    now.setTime(now.getTime() - now.getDate()*24*60*60*1000);
    days += now.getDate(); // <-- now is last day of last month now, so we know how many days there were and add this number
}