Find the 100th day and other milestone dates

The job

Couples mark the 100th day, projects hit the 500th day, a service crosses its 10,000th day of operation. Counting on a calendar is error-prone; the calculator lists every milestone — round day counts and year anniversaries — with the weekday and how far away each is.

How to do it

Pick the start date and run the list. Each row shows the milestone (100 days, 1 year, and so on), the date it lands on with its weekday, and how many days away it is from today — past milestones show as days ago.

• Day milestones run to 30,000 days — roughly 82 years of round-number days.
• Year milestones land on the same month and day each year.
• A Feb 29 start shifts to Feb 28 in common years; those rows are marked.

Worked example

Starting 2024-03-15: the 100th day is 2024-06-23, the 1,000th day is 2024-12-10, and the 1st anniversary is 2025-03-15 — each with its weekday and days-away figure next to it.

Limits

Everything is calendar arithmetic in your time zone — day counts step over midnight regardless of clock time, and anniversaries keep the same month/day. Leap-day starts land on Feb 28 in common years. Start dates are accepted from 1900 to 2200.