Calculate days between two dates, find weekdays vs weekends, week numbers, year progress, and view a monthly calendar grid. Supports any year.
How many days until your deadline? How many business days between two dates? What day of the week was a specific date? This calendar calculator answers all of these questions and more, working with any two dates you provide.
Enter a start and end date to get the complete breakdown: total days, weeks, months, and years between them. The calculator separates weekdays from weekend days (essential for business planning), shows the day of the week for each date, calculates the ISO week number, and displays a visual year progress bar.
The monthly calendar grid highlights your selected date, making it easy to visualize the month at a glance. Whether you're planning a project timeline, counting down to an event, or calculating business days between deadlines, this tool provides every date metric you need. It also keeps the selected month and day in a form that is easy to compare across multi-date planning tasks.
Counting days between dates manually is tedious and error-prone, especially when month lengths, leap years, weekdays, and weekends all matter at once. This calculator handles those date rules in one place and shows the result in the formats people actually use for planning.
It is useful because it gives both the raw interval and the business-day view, so the same date range can be interpreted correctly for scheduling, deadlines, and year-progress tracking.
Days between = |date2 - date1| in milliseconds / 86,400,000. Weekdays counted by iterating and excluding Saturday (6) and Sunday (0). Week number = ceil(dayOfYear / 7). Leap year: divisible by 4 AND (not by 100 OR by 400).
Result: 64 days (9 weeks 1 day), 44 weekdays, 20 weekend days
From January 15 to March 20, 2025 spans 64 calendar days. Of these, 44 are weekdays (Monday-Friday) and 20 are weekend days (Saturday-Sunday). January 15 is a Wednesday, and March 20 is a Thursday.
Calendar math is more complex than it appears. Months have different lengths (28-31 days), leap years add February 29 every four years (with century exceptions), and the Gregorian calendar itself has only been in use since 1582. The modern system uses the proleptic Gregorian calendar for earlier dates, projecting current rules backward even though they didn't historically apply.
Business days (weekdays) are the standard for corporate deadlines, legal filings, shipping estimates, and project management timelines. A common rule of thumb is that one calendar week equals 5 business days, but this breaks down for periods spanning weekends unevenly. Always count explicitly rather than dividing by 7 and multiplying by 5.
ISO week numbers (1-52 or 53) are widely used in European business, manufacturing, and logistics for scheduling. They provide a consistent numbering system that accounts for the fact that years don't start on the same day of the week. Many project management tools, shipping systems, and ERP software reference week numbers rather than dates.
Yes — the calculator shows both total calendar days and weekday (business day) count separately. Weekdays exclude Saturdays and Sundays but do not account for public holidays, which vary by country and region.
The ISO week number is the week of the year according to ISO 8601. Weeks start on Monday, and the first week is the week containing the first Thursday of January. Most of the year, this matches simple week counting.
Yes — the calculator correctly identifies leap years (divisible by 4, except centuries unless divisible by 400). February has 29 days in leap years. The leap year indicator is shown in the year progress output.
The calculator supports any positive year number. For historical dates before the Gregorian calendar adoption (1582), note that the calendar grid uses proleptic Gregorian dates, which may not match historical records.
Projects and deadlines often use business days (excluding weekends), while rentals, interest calculations, and age calculations use calendar days. Having both prevents the common mistake of confusing the two.
Year progress = (day of year / days in year) × 100. Day of year is the running count from January 1. A common year has 365 days; a leap year has 366. This is useful for planning and goal tracking.