Core JavaScript

Calculate Days Between Dates

This JavaScript program shows how to calculate the number of days between two date input elements.

DaysBetweenTwoDates.html

<!DOCTYPE html>
<html>
	<head>
		<title>XoaX.net's Javascript</title>
		<script type="text/javascript" src="DaysBetweenTwoDates.js"></script>
	</head>
	<body>
		<label for="nStartDate">Start Date: <input id="idStartDate" type="date" name="nStartDate" onchange="CalculateDaysBetween()" /></label><br />
		<label for="nEndDate">End Date: <input id="idEndDate" type="date" name="nEndDate" onchange="CalculateDaysBetween()" /></label><br />
		<label for="nDaysBetween">Days Between (including end date): <span id="idBetween" name="nDaysBetween"></span></label>
	</body>
</html>

DaysBetweenTwoDates.js

function CalculateDaysBetween() {

	// Get the start date in milliseconds since 1970 in UTC
	var qStartElement = document.getElementById("idStartDate");
	var sStartValue = qStartElement.value;
	var iStartTimeMs = Date.parse(sStartValue+'T00:00:00.000Z');

	// Get the end date in milliseconds since 1970 in UTC
	var qEndElement = document.getElementById("idEndDate");
	var sEndValue = qEndElement.value;
	var iEndTimeMs = Date.parse(sEndValue+'T00:00:00.000Z');

	// Milliseconds between dates
	var iMsBetween = iEndTimeMs - iStartTimeMs;

	// Conversion to days
	const kiMsPerMinute = 1000 * 60;
	const kiMsPerHour = 60*kiMsPerMinute;
	const kiMsPerDay = 24*kiMsPerHour;
	var iDaysBetween = iMsBetween/kiMsPerDay;
	
	// Display the result
	var qBetweenElement = document.getElementById("idBetween");
	qBetweenElement.innerHTML = iDaysBetween;
}
 

Output

 
 

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