Workdays Calculator

Data Source and Methodology

This tool's date calculations are based on the Gregorian calendar, the international standard for civil use. All date representations and weekday calculations conform to the ISO 8601 standard.

All calculations are performed using a precise day-by-day iteration algorithm. The calculator loops through each day in the specified range and checks it against two user-defined sets of rules:

1. Weekend Days: A list of days of the week (e.g., Saturday, Sunday) to exclude.
2. Holidays: A specific list of calendar dates (e.g., 2025-12-25) to exclude.

The Algorithm Explained

A simple mathematical formula is not sufficient for this task due to the variable nature of weekends and holidays. A rough estimation can be made with LaTeX: $N_{workdays} \approx \lfloor \Delta_{days} \times \frac{5}{7} \rfloor - N_{holidays}$ (Where $\Delta_{days}$ is the total days and $N_{holidays}$ is holidays on weekdays).

This calculator does not use that estimation. It uses a precise iterative algorithm, represented in pseudocode below, to ensure 100% accuracy.

Algorithm for Counting Workdays

function countWorkdays(startDate, endDate, weekends, holidays):
  workdayCount = 0
  currentDate = startDate

  while currentDate <= endDate:
    dayOfWeek = getDay(currentDate)
    isHoliday = holidays.contains(currentDate)
    isWeekend = weekends.contains(dayOfWeek)

    if NOT isWeekend and NOT isHoliday:
      workdayCount = workdayCount + 1
    
    currentDate = addOneDay(currentDate)
  
  return workdayCount

Algorithm for Adding Workdays

function addWorkdays(startDate, daysToAdd, weekends, holidays):
  workdayCount = 0
  currentDate = startDate

  while workdayCount < daysToAdd:
    currentDate = addOneDay(currentDate)
    dayOfWeek = getDay(currentDate)
    isHoliday = holidays.contains(currentDate)
    isWeekend = weekends.contains(dayOfWeek)

    if NOT isWeekend and NOT isHoliday:
      workdayCount = workdayCount + 1
  
  return currentDate

Glossary of Variables

• Start Date: The first day of the period, or the day from which to add/subtract.
• End Date: The last day of the period.
• Include Start/End Date: Checkboxes to determine if the start and end dates themselves should be part of the calculation. By default, we include the end date but not the start date (common for "time until" calculations).
• Workdays (to Add/Subtract): The number of business days to project forward or backward.
• Weekend Days: Days of the week to exclude from all calculations.
• Holidays: Specific calendar dates to exclude. These are treated as non-working days, even if they fall on a weekday.
• Total Workdays: The final count of days that are neither weekends nor holidays.

How It Works: A Step-by-Step Example

Let's calculate the workdays for a project starting on Monday, December 22, 2025, and ending on Friday, January 2, 2026. We want to include both the start and end dates in our count.

• Start Date: 2025-12-22
• End Date: 2026-01-02
• Include Start Date: Yes
• Include End Date: Yes
• Weekends: Saturday, Sunday
• Holidays: 2025-12-25 (Christmas Day), 2026-01-01 (New Year's Day)

The algorithm will iterate as follows:

Result: The total count is 8 workdays.

Frequently Asked Questions (FAQ)