Accurately tracking hours worked is fundamental for payroll, project management, freelancer billing, and labor law compliance.
This calculator simplifies the process of determining the total billable or work hours between a start and end date and time,
while also accounting for any breaks taken during that period.
How it Works: The Math Behind the Calculation
The calculator operates by converting all input dates and times into a common unit (milliseconds since the Unix epoch)
to accurately measure the elapsed time. The steps involved are:
1. Combine Date and Time: The selected start date and time are merged into a single datetime object, and the same is done for the end date and time.
2. Calculate Total Elapsed Time: The difference between the end datetime and the start datetime is calculated. This gives the gross elapsed time in milliseconds.
3. Convert to Hours: The total elapsed milliseconds are converted into hours by dividing by the number of milliseconds in an hour (1000 ms/s * 60 s/min * 60 min/hr = 3,600,000 ms/hr).
4. Subtract Break Time: The duration of breaks, provided in minutes, is converted into hours (minutes / 60) and then subtracted from the gross hours to get the net total hours worked.
The formula can be summarized as:
Total Hours = ( (End Datetime - Start Datetime) in milliseconds / 3,600,000 ) - (Break Duration in minutes / 60)
Use Cases for Tracking Hours Worked
Employees: For accurate payroll processing, ensuring fair compensation for all hours, including overtime.
Freelancers & Contractors: To bill clients precisely for the time spent on projects, fostering transparency and trust.
Project Managers: To monitor project timelines, allocate resources effectively, and track team productivity.
Students: For tracking study hours for specific subjects or assignments, helping to manage academic workload.
Timesheet Compliance: Ensuring that recorded hours meet legal requirements and company policies.
Example Calculation
Let's say an employee starts their shift on October 26, 2023, at 9:00 AM and finishes on the same day at 5:30 PM.
They took a 45-minute break during their shift.
Start Datetime: 2023-10-26 09:00
End Datetime: 2023-10-26 17:30
Break Duration: 45 minutes
The total elapsed time from 9:00 AM to 5:30 PM is 8 hours and 30 minutes, which is 8.5 hours.
Subtracting the break: 8.5 hours – (45 minutes / 60 minutes/hour) = 8.5 hours – 0.75 hours = 7.75 hours.
This calculator automates this process for any date range.
function calculateTotalHours() {
var startDateInput = document.getElementById("startDate");
var startTimeInput = document.getElementById("startTime");
var endDateInput = document.getElementById("endDate");
var endTimeInput = document.getElementById("endTime");
var breakDurationInput = document.getElementById("breakDurationMinutes");
var totalHoursOutput = document.getElementById("totalHours");
var startDate = startDateInput.value;
var startTime = startTimeInput.value;
var endDate = endDateInput.value;
var endTime = endTimeInput.value;
var breakDurationMinutes = parseInt(breakDurationInput.value);
if (!startDate || !startTime || !endDate || !endTime) {
totalHoursOutput.innerHTML = "Please fill in all date and time fields.";
return;
}
var startDateTimeStr = startDate + "T" + startTime + ":00";
var endDateTimeStr = endDate + "T" + endTime + ":00";
var start = new Date(startDateTimeStr);
var end = new Date(endDateTimeStr);
if (isNaN(start.getTime()) || isNaN(end.getTime())) {
totalHoursOutput.innerHTML = "Invalid date or time format.";
return;
}
if (end 0) {
breakDurationHours = breakDurationMinutes / 60; // Convert minutes to hours
}
var totalHoursWorked = elapsedHours – breakDurationHours;
if (totalHoursWorked < 0) {
totalHoursWorked = 0; // Ensure we don't show negative hours
}
totalHoursOutput.innerHTML = totalHoursWorked.toFixed(2); // Display with 2 decimal places
}