As a full birth date might be considered personally identifiable information, using only the birth year or year and month of birth is a good alternative. It is still possible to calculate the age from these variables using a calculation field (although with less precision).

Calculate the age of a patient from a birth year

var a = moment();
var b = moment('{dem_pat_birthyear}', 'YYYY');
var diff = a.diff(b, 'years'); // calculates patient's age in years
diff; // this prints out the age

In this calculation {dem_pat_birthyear} will need to be replaced with your variable name for birth year.

Note: In the first line, moment(); is used to automatically calculate today's date. This date will be updated once the data entry for a record is opened.

Calculate the age from a birth year and a month using a text field

If you are using a text field to collect only month and year of birth, you can use the following template to calculate the age:

var a = moment();
var b = moment('{dem_pat_birthyear}', 'MM-YYYY');
var age = moment.duration(a.diff(b));
var years = age.years();
var months = age.months();
"The age is " + years + " years " + months + " months ";

In this calculation {dem_pat_birthyear} will need to be replaced with your variable name for birth year.

Calculate the age of a patient from the birth year and a visit date

var birthyear = moment('{patient_birthyear}', 'YYYY');
var visitdate = moment('{baseline_visit}', 'DD-MM-YYYY');
visitdate.diff(birthyear, 'y');

In this calculation {patient_birthyear} will need to be replaced with your variable name for birth year and {baseline_visit} for the visit date. Test this calculation in the calculation helper.

Calculate the age of a patient from a birth year and display it in years in months

When you want to show age in years and months, for example for children, you can use the following formula.

var date1 = "{dob}".split("-");
var jsdate1 = new Date(date1 [2], date1 [1]-1, date1 [0], 0, 0, 0);
var date2 = "{visit_date}".split("-");
var jsdate2 = new Date(date2 [2], date2 [1]-1, date2[0], 0, 0, 0);
var diff = Math.floor(jsdate2.getTime() - jsdate1.getTime());
var day = 1000 * 60 * 60 * 24;
var days = Math.floor(diff/day);
var months = Math.floor(days/31);
var years = Math.floor(months/12);
months = months - (12*years)
years + " years, "+ months + " months";

You can test this template in the calculation helper.

Calculate the age of a patient from a birth year and birth month and display age in years

var string = '{birthmonth}' + '-' + '{birthyear}';
var dob = moment(string, 'MM-YYYY');
var date = moment('{date_compl}', 'DD-MM-YYYY');
var diff = date.diff(dob, 'y');
diff;

In this calculation {birthmonth} and {birthyear} will need to be replaced with your variables name for birth year and birth month. You can also test this calculation in the calculation helper tool.