Date, Days, Weeks & Months Calculator
Using the Calendar Calculator is very simple:
Calendar Calculator is widely used in various situations from daily life to business:
Calculate the number of days from project start to deadline, or determine how many days after a specific milestone the next deadline occurs. For example, easily calculate "What date is 90 business days after the start date?"
When verifying contract validity periods, calculate the exact number of days, months, and years from start to end date. Accurately determine expiration dates for 1-year, 3-month contracts, etc.
Count down the remaining days to wedding anniversaries, birthdays, and event dates. Instantly calculate "How many days until our 10th anniversary" or "How many weeks until my birthday."
Accurately calculate current age from date of birth, or calculate years of service from hire date. Also possible to calculate "How many days have I lived" or "How many days until retirement."
Enter departure and return dates to calculate stay duration. Convenient for long vacation planning and visa stay period verification.
Calculate payment deadlines (e.g., 30 days from issue date) from invoice issue date, or check remaining days until payment deadline. Perfect for managing expected payment dates.
Can be used for calculating pregnancy period (280 days from last menstrual period), managing medication periods, and scheduling medical appointments.
Calendar calculation refers to calculating the period between dates or adding/subtracting a certain period to/from a specific date. Though it seems simple, the following complex elements must be handled accurately:
Normal years have 365 days, but leap years have 366 days. Leap years occur every 4 years, but years divisible by 100 are common years, except years divisible by 400 which are leap years (e.g., 2000 is a leap year, 1900 is a common year). Calendar calculations must accurately process these rules.
January has 31 days, February has 28 days (29 in leap years), April has 30 days, etc. - the number of days varies by month. When calculating "3 months later," these differences must be considered.
Calculating only business days (working days) excluding weekends and holidays is also important. Used for project actual working days and payment deadline business day calculations.
For international projects, time zone differences and daylight saving time transitions must also be considered.
In contracts, legal documents, and financial transactions, date calculation errors can cause serious problems. Using accurate calendar calculation tools helps avoid such risks.
Manually counting on calendars takes time and errors occur easily. Calendar Calculator automatically considers leap years and month-end dates, providing instant accurate results.
By counting only business days excluding weekends, accurately grasp actual business days. Improves accuracy of project management and task estimation.
Display the same period simultaneously in "days," "weeks," "months," and "years," allowing selection of the optimal unit according to purpose.
Instantly calculate dates like "90 days from today" or "3 months before contract date," making schedule management more efficient.
Ready to use with just a browser. No software installation or registration required, completely free to use.
All calculations are completed in the browser, and no data is sent to servers. Contract information and personal anniversaries can be calculated with confidence.
For example, if you have "weekly Monday meetings," calculate days from today to the next meeting to understand preparation time.
When calculating deadlines for multiple projects at once, efficiently open multiple browser tabs and calculate in parallel.
By registering dates calculated with Calendar Calculator in calendar apps like Google Calendar or Outlook, schedule management becomes more reliable.
Saving calculation results as screenshots is convenient for later reference. Can also be used as evidence for contract periods.
Yes, leap years are processed accurately. The leap year determination rules (every 4 years, but years divisible by 100 are common years, years divisible by 400 are leap years) are fully implemented. Periods including February 29 are calculated correctly.
Yes, business day calculation is supported. Actual working days excluding weekends can be counted. However, since holidays vary by country, calculations excluding holidays require manual adjustment.
Yes, past dates can also be calculated. For example, calculations like "How many days have passed since birth" or "What date was it 1 year ago" are possible.
Yes, it changes. When the "Include End Date" option is on, the end date itself is also counted. For example, from January 1 to January 3, including gives 3 days, excluding gives 2 days. For contracts, confirm whether it's "including the day" or "from the next day."
Very distant future or past dates can be calculated, but practical use within about 100 years is recommended. Due to JavaScript Date object limitations, accuracy may decrease for dates far from January 1, 1970.
Month addition maintains the day of the base date. For example, 3 months after January 31 is April 30 (since April 31 doesn't exist), 1 month after February 28 is March 28.
Once the page is loaded, calculations are completed in the browser, so calculations themselves are possible even if internet connection is lost. However, connection is required for page reloads.
In the current version, calculation results are manually copied and pasted. Screenshots can also be taken and saved. CSV export functionality is being considered for the future.
Convert between time units: seconds, minutes, hours, days, etc.
Convert between Unix timestamp and ISO 8601 format
Convert times between different locations worldwide