How to use the date calculator
Pick a tab and results update as you type. Tap a date field to open your phone’s calendar, or press Today.
- Between: the number of days between two dates, plus years-months-days, weeks, weekdays and hours.
- Add days: the date N days, weeks, months or years after (or before) a date. Quick buttons cover 30, 90 and 100 days, 6 months and more.
- Countdown: save several countdowns (D-) and count-ups (D+). Relationship and baby presets list 100-day milestones and anniversaries automatically.
- Workdays: count business days in a range or find the date N business days away, skipping weekends (and South Korean public holidays if you choose).
Should the start date be included?
By default the start date is not counted: from October 1 to October 8 is 7 days. This is how elapsed time, deadlines and interest periods are usually counted.
Turn on Include start date to count both ends, which makes the same range 8 days. Anniversaries counted from the first day work this way: if you got together on January 1, your 100th day is April 10 (January 1 + 99 days).
How months are counted
Months are counted as the largest number N for which "the same day N months later" does not pass the end date. If a month has no such day, the last day of that month is used: one month after January 31 is February 28 (or 29 in a leap year), and one month after March 31 is April 30. With the start date included, January 1 to January 31 is exactly one month.
Countdowns, milestones and privacy
Saved countdowns stay in this browser only and are never uploaded. To open one on another device or share it with someone, press Share link; the recipient can add it to their own list with one tap.
Milestones include every 100 days up to 1,000, then 1,500, 2,000, 3,000 and up to 10,000 days, plus yearly anniversaries, sorted by date with the next one highlighted.
The due-date preset uses Naegele’s rule (first day of the last period + 280 days). Cycles longer or shorter than 28 days and ultrasound dating can change the actual due date, so follow your clinician’s advice.
FAQ
How many days are between two dates?
Enter both dates in the Between tab. The result counts the days after the start date up to and including the end date. Turn on "Include start date" to add one day.
How do I find the date 90 days from today?
Open the Add days tab, press Today, type 90 (or tap the 90 days button) and the date appears instantly with its weekday.
What is one month after January 31?
February has no 31st, so the calculator uses the last day of February (28th, or 29th in a leap year) and tells you it did so.
Are holidays excluded from business days?
Weekends are excluded by default. You can also exclude South Korean public holidays (official lists for 2024–2027, estimates for other years). Other countries’ holidays are not included.
Where are my countdowns saved?
Only in your current browser. Nothing is sent to a server. Clearing site data removes them, so use Share link to move a countdown to another device.