Date Calculator

Understanding Date Calculations

Date calculations are essential for planning events, tracking milestones, calculating ages, and managing deadlines. Our date calculator handles all types of date arithmetic with precision, accounting for leap years and varying month lengths.

How Date Calculations Work

Calculating days between dates requires accounting for several factors:

• Leap Years: Years divisible by 4 (except centuries not divisible by 400) have 366 days
• Varying Month Lengths: Months have 28-31 days depending on the month and leap year status
• Time Zones: Our calculator uses UTC midnight to avoid timezone confusion
• Business Days: Excludes Saturdays and Sundays for workplace planning

Common Use Cases

1. Calculate Days Until an Event

Planning a wedding, vacation, or project deadline? Use "Days Between" mode with today's date and your event date. You'll see exactly how many days, weeks, and months remain, plus business days for work planning.

2. Project Timeline Planning

Need to know when a 90-day project will complete? Use "Add Days" mode from your start date. Business days show actual working days, helping you set realistic deadlines that exclude weekends.

3. Age Calculation

Want to know your exact age in days? Use "Days Between" with your birthdate and today. Great for celebrating 10,000-day birthdays or tracking how long you've been alive.

4. Historical Date Research

How many days between historical events? Calculate the time span between the moon landing and today, or between any two dates in history. Perfect for students, historians, and trivia enthusiasts.

5. Legal and Financial Deadlines

Many contracts and laws specify "within 30 days" or "90 days from signing." Our calculator helps ensure you meet legal deadlines by showing the exact target date.

6. Pregnancy Due Date Validation

Verify pregnancy due dates by calculating 280 days (40 weeks) from the last menstrual period. Cross-reference with your doctor's estimate to understand your timeline.

Business Days vs Calendar Days

Calendar Days	Business Days	Weekend Days	Common Use Case
7 days	5 days	2 days	1 week project
14 days	10 days	4 days	2-week sprint
30 days	~22 days	~8 days	Monthly project
90 days	~65 days	~25 days	Quarterly planning
365 days	~260 days	~105 days	Annual project

Understanding Leap Years

Leap years add complexity to date calculations. A year is a leap year if:

• Divisible by 4 (e.g., 2024, 2028)
• Except if divisible by 100 (e.g., 1900 was NOT a leap year)
• Unless also divisible by 400 (e.g., 2000 WAS a leap year)

Leap years have 366 days instead of 365, with February having 29 days. Our calculator automatically accounts for all leap years in your date range for precise results.

Quick Reference: Days in Each Month

Month	Days	Notes
January	31	Q1
February	28 or 29	29 in leap years
March	31	Q1
April	30	Q2
May	31	Q2
June	30	Q2
July	31	Q3
August	31	Q3
September	30	Q3
October	31	Q4
November	30	Q4
December	31	Q4

Tips for Date Planning

• Use Business Days for Work: When estimating project timelines, use business days to account for weekends
• Add Buffer Time: For important deadlines, calculate the date and add 2-3 days buffer
• Check Holidays: Our calculator doesn't account for holidays - subtract them manually
• Time Zones Matter: For global projects, be aware of date line differences
• Month-End Dates: If adding months, some months are shorter (e.g., Jan 31 + 1 month = Feb 28/29)
• Recurring Events: Calculate once, then add 7 days (weekly), 30 days (monthly), or 365 days (yearly)

Historical Calendar Changes

Note: The Gregorian calendar (current standard) was adopted in 1582. Before then, the Julian calendar was used. October 1582 "skipped" 10 days (Oct 4 → Oct 15) when switching calendars. For dates before 1582, historical calculations may differ from modern astronomical calculations.