Date Calculator - Calculate Date Difference, Add or Subtract Days Online Free
Date Calculator - Calculate days between dates, add or subtract time, and find weekday information instantly.
Add or Subtract Date
Weekday & Date Information
Understanding Date Calculations
What is a Date Calculator?
A date calculator is a tool that performs arithmetic operations on calendar dates. Unlike simple math calculators, date calculators account for varying month lengths (28-31 days), leap years, and calendar system rules.
Our calculator uses the Gregorian calendar, the most widely used civil calendar worldwide, adopted in 1582 and now standard in most countries. It handles complex calculations like "What date is 3 months and 15 days from today?" or "How many days until Christmas?" instantly and accurately.
The Gregorian Calendar System
The Gregorian calendar reformed the Julian calendar to better align with Earth's orbit around the sun. A standard year has 365 days, with leap years adding a 366th day every 4 years (with exceptions for century years).
- • 31 days: Jan, Mar, May, Jul, Aug, Oct, Dec
- • 30 days: Apr, Jun, Sep, Nov
- • 28/29 days: Feb (29 in leap years)
- • Leap year rule: Divisible by 4, except centuries (unless divisible by 400)
Common Use Cases
Age Calculation
Calculate exact age in years, months, and days. Find out how many days you've been alive or plan milestone celebrations with precision.
Event Planning
Calculate event countdowns, set reminder dates, plan project timelines, and schedule meetings by adding or subtracting specific durations.
Business Days
Calculate working days between dates, excluding weekends. Essential for project management, contract deadlines, and delivery estimates.
Vacation Planning
Calculate vacation duration, plan return dates, count days off, and schedule time away from work with accurate day counts.
Legal & Financial
Calculate contract periods, loan durations, grace periods, payment due dates, and statute of limitation deadlines accurately.
Academic Calendar
Calculate semester lengths, days until exams, graduation countdowns, and school break durations for better academic planning.
Date Calculation Tips & Tricks
Understanding Leap Years
Leap years occur every 4 years to keep the calendar synchronized with Earth's orbit. However, century years (1700, 1800, 1900) are NOT leap years unless divisible by 400 (2000, 2400 ARE leap years).
Example: February 2024 has 29 days (leap year), but February 2100 will have only 28 days (not a leap year, despite being divisible by 4).
Business Day Calculations
Business days typically exclude weekends (Saturday and Sunday). Our calculator shows weekday count separately. For accurate business day calculations including holidays, you'll need to manually subtract public holidays specific to your region.
Tip: The U.S. has 10 federal holidays. Subtract these from the weekday count for accurate working day estimates.
Date Arithmetic Gotchas
Adding "1 month" to January 31st gives February 28th (or 29th in leap years), not March 2nd or 3rd. This is because February doesn't have 31 days. Our calculator handles these edge cases correctly, adjusting to the last valid day of the target month.
Frequently Asked Questions
How do I calculate the number of days between two dates?
Use the Date Difference Calculator: 1) Enter your start date, 2) Enter your end date, 3) Check 'Include end day' if needed, 4) The result shows years, months, days, total days, weekdays, and weekend days automatically. Our calculator includes a detailed breakdown showing exact time periods.
How do I add days to a date?
Use the Add/Subtract Calculator: 1) Enter your start date, 2) Click 'Add (+)', 3) Enter the number of years, months, weeks, and days to add, 4) The result date displays immediately with the exact date and total days added. You can mix different time units (e.g., 1 year 6 months 2 weeks).
What day of the week was I born?
Use the Weekday Finder: 1) Enter your birthdate, 2) The calculator instantly shows the weekday (Monday-Sunday), week number of that year, day of year, and which quarter it falls in. You can also see if it was a weekend day.
Does the calculator account for leap years?
Yes! Our date calculator automatically accounts for leap years (366 days) and regular years (365 days) when calculating date differences or adding/subtracting time. The Gregorian calendar rules are fully implemented, ensuring accurate calculations across centuries.
How many business days are between two dates?
The Date Difference Calculator shows both weekdays (Monday-Friday) and weekend days separately. The 'Weekdays' count gives you the number of business days, excluding Saturdays and Sundays. Note: This does not account for public holidays, which vary by region.
Can I subtract dates to find age?
Yes! Enter your birthdate as the start date and today's date as the end date in the Date Difference Calculator. The result shows your exact age in years, months, and days. For a more detailed age calculation with next birthday countdown, use our dedicated Age Calculator.
What is the 'Include end day' option?
By default, the calculator counts from start date up to (but not including) the end date. Checking 'Include end day' adds 1 day to the count. Example: Jan 1 to Jan 5 normally gives 4 days, but with 'Include end day' checked, it gives 5 days.
How accurate is the date calculator?
Our date calculator is 100% accurate and follows the Gregorian calendar system used worldwide. It correctly handles leap years, month lengths (28-31 days), and all calendar edge cases. Calculations are performed using JavaScript's native Date object with additional validation.