Date calculator

How to use it

1. Choose a calculation and enter the dates. Results update as you type.
2. For milestones, count the starting day as day 1 and select the day counts or anniversaries you need.
3. To shift a date, add rows with a sign, amount and unit. Copy any result using its adjacent button.

Details

The countdown compares a target date with today in your device’s timezone. D− means the date is ahead, D+ means it has passed, and D-Day means today. Counting the starting day as day 1 adds one to both elapsed and remaining counts. Milestone dates use the target date as their starting point: the 100th day is 99 days later, while a one-year anniversary advances the calendar year.

A date interval excludes the end date unless you choose to include it. Weeks are groups of seven days; calendar months and years are not fixed numbers of days. The calculator finds the largest whole-month offset from the original start that fits within the interval, clamps missing dates to month end, then counts the remaining days. This can differ from treating every month as 30 days.

Date adjustments run from top to bottom. Adding one month twice to January 31, 2023 gives March 28; adding two months in one row gives March 31. Age counts completed birthdays as of the reference date. A February 29 birthday is treated as February 28 in common years. Dates from year 1 through 9999 use the Gregorian calendar. Time of day is ignored, and day differences use UTC midnight so daylight saving changes cannot add or remove a day. Your entries stay in this page’s memory and are not stored or added to the address.