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How to Calculate the Day of the Week from a Date and Actual Time Spent Between Two Date-Times in Apex

When working with Salesforce, there are instances where we need to compute the day of the week from a given date or determine the actual time spent between two date-time values, considering only business hours.

For example, if we need to track the exact amount of time a user spent on a Lead, Case, or Task, simply subtracting two date-time values won't suffice if we need to exclude non-working hours.

In this post, we will cover:
  • How to determine the day of the week from a given date in Apex.
  • How to calculate actual time spent between two date-times, while considering business hours (Monday to Friday: 8 AM - 8 PM, Saturday & Sunday: 8 AM - 4:30 PM).

1. How to Determine the Day of the Week from a Date in Apex

Salesforce does not provide a direct method to get the day name (Monday, Tuesday, etc.) from a Date field. However, we can achieve this using toStartOfWeek() and daysBetween() methods.

public static String getDayOfWeek(Date inputDate) {
    // Get the start of the week (Sunday) for the given date
    Date startOfWeek = inputDate.toStartOfWeek();
   
    // Calculate the difference in days between the input date and the start of the week
    Integer dayDifference = inputDate.daysBetween(startOfWeek);
   
    // Determine the day of the week based on the difference
    String dayOfWeek;
    switch on dayDifference {
        when 0 { dayOfWeek = 'Sunday'; }
        when 1 { dayOfWeek = 'Monday'; }
        when 2 { dayOfWeek = 'Tuesday'; }
        when 3 { dayOfWeek = 'Wednesday'; }
        when 4 { dayOfWeek = 'Thursday'; }
        when 5 { dayOfWeek = 'Friday'; }
        when 6 { dayOfWeek = 'Saturday'; }
        when else { dayOfWeek = 'Invalid'; }
    }
   
    return dayOfWeek;
}

How It Works

  • toStartOfWeek() returns the Sunday of that week.
  • daysBetween() calculates how many days exist between the input date and that Sunday.
  • The day difference helps us map the date to its respective weekday.

Example Output

System.debug(getDayOfWeek(Date.newInstance(2025, 3, 19))); // Output: "Wednesday"

System.debug(getDayOfWeek(Date.newInstance(2025, 3, 23))); // Output: "Sunday"

2. How to Calculate Actual Time Spent Between Two Date-Times Excluding Off-Hours

If we need to calculate the actual time spent within business hours, we must:

  1. Loop through each date in the range.
  2. Identify if the day is a weekday (Monday-Friday, 8 AM - 8 PM) or weekend (Saturday-Sunday, 8 AM - 4:30 PM).
  3. Consider only the hours that fall within the defined working schedule.
public static Decimal calculateBusinessHours(Datetime startDateTime, Datetime endDateTime) {
    if (startDateTime == null || endDateTime == null) {
        return 0;
    }      
   
    Date startDate = startDateTime.date();
    Date endDate = endDateTime.date();    
    Decimal totalHours = 0;
   
    // Loop through each date from start to end
    for (Date currentDate = startDate; currentDate <= endDate; currentDate = currentDate.addDays(1)) {
        // Determine the day of the week (0 = Sunday, 6 = Saturday)
        Date startOfWeek = currentDate.toStartOfWeek();
        Integer dayDifference = currentDate.daysBetween(startOfWeek);
       
        // Define business hours start time (8 AM)
        Datetime businessStart = Datetime.newInstance(currentDate, Time.newInstance(8, 0, 0, 0));
        Datetime businessEnd;
       
        // Set business end time based on weekday/weekend
        if (dayDifference == 6 || dayDifference == 0) { // Weekend (Saturday = 6, Sunday = 0)
            businessEnd = Datetime.newInstance(currentDate, Time.newInstance(16, 30, 0, 0)); // 4:30 PM
        } else {
            businessEnd = Datetime.newInstance(currentDate, Time.newInstance(20, 0, 0, 0)); // 8:00 PM
        }
       
        // Determine effective start and end time for this date
        Datetime effectiveStart = (startDateTime > businessStart) ? startDateTime : businessStart;
        Datetime effectiveEnd = (endDateTime < businessEnd) ? endDateTime : businessEnd;
       
        // If within business hours, calculate time difference
        if (effectiveStart < effectiveEnd) {
            totalHours += (effectiveEnd.getTime() - effectiveStart.getTime()) / (1000 * 60 * 60); // Convert ms to hours
        }
    }
   
    return totalHours;
}

How It Works

  1. Loops through each date between startDateTime and endDateTime.
  2. Determines whether the day is a weekday or weekend using daysBetween().
  3. Sets business start and end times accordingly:
    • Weekdays (Mon-Fri): 8 AM - 8 PM
    • Weekends (Sat-Sun): 8 AM - 4:30 PM
  4. If startDateTime is before business hours, it adjusts to 8 AM.
  5. If endDateTime is after business hours, it adjusts to closing time.
  6. Calculates the time difference for each day within business hours.

Example Usage & Output

Datetime startDT = Datetime.newInstance(2025, 3, 18, 10, 0, 0); // March 18, 2025 - 10:00 AM
Datetime endDT = Datetime.newInstance(2025, 3, 19, 15, 30, 0); // March 19, 2025 - 3:30 PM
System.debug(calculateBusinessHours(startDT, endDT));

Expected Output:
If March 18 and 19 are weekdays:

  • 10:00 AM - 8:00 PM (Day 1) → 10 hours
  • 8:00 AM - 3:30 PM (Day 2) → 7.5 hours
  • Total Business Hours: 17.5 hours

Conclusion

By leveraging Apex logic, we can: 

✅ Determine the day of the week from a date
✅ Calculate actual time spent between two date-times while excluding non-working hours
✅ Handle weekday/weekend variations dynamically

This approach is useful in Lead tracking, Case management, Worklogs, and SLAs where accurate time calculation within business hours is required.

Would you like to extend this further with public holidays exclusion? Let me know in the comments!

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