age calculation in javascript a javascript function to get the number of years passed since someone's birthday... i.e. age, is a useful and commonly sought-after addition to a web-designers toolbox. the following function simply subtracts the difference in years between now and the birthdate in question, and then adjusts it by a year if the month and day of the birthday fall earlier in the year. it doesn't validate the date, and it only deals in whole number years meaning babies ages in months are not considered. <script language="javascript"> function getage(birthdate) { //** by jasonwheeler.com **// //** out of courtesy, please retain this notice **/ // //expects uk format dd/mm/yyyy splitbirthdayparts = birthdate.split('/'); myday=splitbirthdayparts[0]; mymonth= splitbirthdayparts[1]; myyear = splitbirthdayparts[2]; //note; if date in us format, then myday // would be splitbirthdayparts[1] and mymonth // would be splitbirthdayparts[0] //now get today's values var age; var today = new date(); var todaysday = today.getdate(); var todaysmonth = today.getmonth()+1; //1 is added as getmonth() returns a zero-based // value, i.e. 0=january, 1=february, 11=december var todaysyear = today.getyear(); //now get base difference in years age=todaysyear-myyear; //if 'now' is earlier in the year month-wise than //the birthday supplied, then adjust age by a year if (todaysmonth<mymonth) age--; if (todaysmonth==mymonth) { //if 'now' is in same month, but earlier // in that month than the birthday supplied // then adjust age by a year if (todaysday<myday) age--; } //ok age should now correct year-wise. //if all screws up, then fail safe the output. :) //0 could be substituted depending on //application needs if (isnan(age)) age="???"; return age; } </script> to use this function in your web-page, copy the above script snippet and paste it before the </head> tag. you can then call the function from any point by passing the function a date string in the format dd/mm/yyyy. in the following example, the onblur event is used on a date entry text box, and the result updates an adjacent div. <!--typical date entry text box with the onblur event used to trigger the age update--> <input type="text" id="txt_date_of_birth" name="txt_date_of_birth" onblur="document.getelementbyid('div_age').innerhtml='age:' + getage(this.value) + ' years';"> <!--an adjacent div with the display style set to inline to make it sit on end of text box--> <div id="div_age" name="div_age" style="display:inline;">age:??? years</div> also in php! return to javascript articles