Calculate days between dates or add/subtract days from a specific date.
Result:
Use a negative number to subtract days (e.g., -15).
New Date:
Understanding Date Counts and Durations
A date count calculator is an essential tool for project managers, event planners, and legal professionals. It allows you to precisely determine the number of days between two specific calendar dates or project into the future by adding a specific duration to a current date.
How to Calculate Days Between Two Dates
Calculating the difference between dates sounds simple, but calendar variations make it tricky. To calculate manually:
Count the remaining days in the start month.
Add the total days for every full month in between.
Add the days elapsed in the final month.
Account for leap years if the duration spans February 29th.
Why Use a Date Calculator?
Project Management: Track milestones and ensure deadlines are met within a specific sprint or phase.
Legal Deadlines: Calculate "statute of limitations" or response times which often depend on a strict count of days.
Personal Milestones: Find out exactly how many days until your next vacation or how many days old you are.
Billing Cycles: Determine pro-rated costs based on the exact number of days a service was active.
Practical Example
Suppose you start a project on January 15th and it is due on April 20th. Using our calculator:
Total Days: 95 days (excluding the end date).
Total Days: 96 days (including the end date).
In weeks: 13 weeks and 4 days.
function calculateDateDiff() {
var startVal = document.getElementById('startDate').value;
var endVal = document.getElementById('endDate').value;
var includeEnd = document.getElementById('includeEndDate').checked;
if (!startVal || !endVal) {
alert("Please select both start and end dates.");
return;
}
var start = new Date(startVal);
var end = new Date(endVal);
// Set both to midnight to avoid DST issues
start.setHours(0, 0, 0, 0);
end.setHours(0, 0, 0, 0);
var diffTime = end.getTime() – start.getTime();
var diffDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
if (includeEnd) {
diffDays += 1;
}
var resultDiv = document.getElementById('diffResult');
var totalDaysP = document.getElementById('totalDaysResult');
var breakdownP = document.getElementById('breakdownResult');
resultDiv.style.display = 'block';
var absDays = Math.abs(diffDays);
var label = diffDays < 0 ? " ago" : "";
totalDaysP.innerText = absDays + " Days" + label;
var weeks = Math.floor(absDays / 7);
var remainingDays = absDays % 7;
breakdownP.innerHTML = "Breakdown: " + weeks + " weeks and " + remainingDays + " days.";
}
function calculateNewDate() {
var baseVal = document.getElementById('baseDate').value;
var offsetVal = document.getElementById('daysOffset').value;
if (!baseVal || offsetVal === "") {
alert("Please select a start date and enter the number of days.");
return;
}
var baseDate = new Date(baseVal);
var offset = parseInt(offsetVal);
// Add the days
baseDate.setDate(baseDate.getDate() + offset);
var options = { weekday: 'long', year: 'numeric', month: 'long', day: 'numeric' };
var resultString = baseDate.toLocaleDateString(undefined, options);
document.getElementById('addResult').style.display = 'block';
document.getElementById('finalDateResult').innerText = resultString;
}
// Set default dates to today for convenience
window.onload = function() {
var today = new Date().toISOString().split('T')[0];
document.getElementById('startDate').value = today;
document.getElementById('baseDate').value = today;
};