OTTERDAY / DATE
Date and business day calculator
Count days, add or subtract days, share a D-day countdown, exclude public holidays, and calculate age.
Result
Choose your dates and calculate.
Dates, birth dates, shifts and rates stay in this tab; they are not sent to a server or saved in browser storage. A D-day link you create contains its target date and title, readable by recipients. Manage exported CSV and print files yourself.
A few helpful answers
How are date boundaries counted?
Choose whether to include each endpoint. The default includes start and excludes end. The same date counts as one only if both are included. Add/subtract and D-day use the plain date difference.
Which holidays and age rules apply?
South Korean, US federal and Japanese holidays cover 2026–2027; local and company closures are excluded. Completed age increases on birthdays, or March 1 in common years for February 29 births. Some Korean laws have special age rules.
Are dates or countdowns saved to a server?
Inputs stay in the tab. D-day sharing puts the target date and title after # in the URL, without sending them to the server. Recipients can read the link contents. Offline calculation works after the initial cache completes.