Add days and months to date

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var lastMestrualDate = document.getElementById('LastMestrualDate').value; var date = new Date(lastMestrualDate); var newdate = new Date(date); newdate.setDate(date.getDate() + 7); newdate.setMonth(newdate.getMonth() + 9); document.getElementById('EDD').value = newdate.getDay() + '/' + newdate.getMonth() + '/' + newdate.getFullYear();