Tryit Editor v2.7

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<!DOCTYPE html>
<html>
<body>

Date: <input type="date" id="myDate" value="2014-05-05">

<p>Click the button to decrement the value of the date field by 5 days (each time you click).</p>

<button onclick="myFunction()">Try it</button>

<p><strong>Note:</strong> The stepDown() method is not supported by Internet Explorer.</p>
<p><strong>Note:</strong> input elements with type="date" are not supported in Internet Explorer or Firefox.</p>

<script>
function myFunction() {
    document.getElementById("myDate").stepDown(5);
}
</script>

</body>
</html>