Date Calculator

Calculate the days between two dates, find a date by adding or subtracting time, and count down to a specific D-Day.

Select dates to calculate instantly · All calculations are processed in your browser only

Difference Between Two Dates

—

—Total Days (Difference)

—Days Including Start Date

—Business Days (Excluding Weekends)

—Weekend Days (Sat·Sun)

—Number of Weeks

—Number of Months

Add · Subtract Dates

Base Date Unit = —

D-Day (Until Target Date)

Target Date —

Calculate Full Age

Date of Birth —

—Full Age

—Full Age (Months)

—Days Since Birth

—Until Next Birthday

💡 Full Age follows the Korean age unification law enacted in June 2023. If your birthday has passed, it's current year − birth year; if not, subtract 1 from that result.

⚠️ Business days are calculated by excluding Saturdays and Sundays only. Public holidays like Lunar New Year and Chuseok, temporary holidays, and company-specific days off are not reflected. Please subtract these separately when determining actual working days.

What is the Date Calculator?

Wondering how many days are left until an anniversary, or the exact time between two dates? This calculator instantly finds the total days, business days (weekends excluded), weeks, and months. You can also add or subtract time from a date, set a D-Day countdown, or find your precise age. Just pick a date or type a number, and the results appear immediately. All calculations are performed in your browser, so any dates you enter remain completely private.

How to use

In the ‘Difference Between Two Dates’ section, select a ‘Start Date’ and an ‘End Date’ to see the duration calculated as total days, business days, weeks, and more.
Under ‘Add · Subtract Dates’, pick a ‘Base Date’, enter an amount (like 100), and choose a ‘Unit’ (Day, Week, etc.) to find the resulting date.
For a countdown, go to ‘D-Day (Until Target Date)’ and choose your ‘Target Date’ to see the remaining (D-) or elapsed (D+) days.
Enter your ‘Date of Birth’ in the ‘Calculate Full Age’ section to find your current age, days since birth, and time until your next birthday.
Use the ‘Today’ button to quickly enter the current date, and the ‘Copy’ button to grab any calculated result.

Frequently asked questions

How do I include the start date in the day count?

The ‘Total Days (Difference)’ result shows the number of full 24-hour periods. For a count that includes the start day, please use the ‘Days Including Start Date’ result shown just below it.

Does the business day calculation account for public holidays?

No. The ‘Business Days’ count is calculated by excluding only Saturdays and Sundays. It does not account for national or local public holidays, which you will need to subtract manually.

Is it safe to enter personal dates like my birthday?

Yes, it is completely safe. All calculations are performed entirely within your web browser. No dates or other information you enter are ever sent to our servers, ensuring your privacy.

What happens if I add 1 month to January 31?

The calculator automatically adjusts for months with fewer days. Adding one month to January 31 results in February 28 (or 29 in a leap year), the last day of the following month.