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100-Day & Anniversary Calculator
Enter a start date and get the 100th, 200th, 300th, one-year, 500th and 1000th day dates.
Favorite it to find it fast on home
When to use it
Start 1 Jan 2026 → 100th day is 10 Apr 2026
Check a one-year or 1,000-day anniversary
Plan a gift before the date arrives
How to use it
1Step 1Fill in Start date
2Step 2Change a value and the result updates instantly
3Step 3Save or copy the result with Calculate
If the result looks off
The result looks wrong
Check the units and the baseline first. Changing a value updates the result instantly.
I want the starting values back
Press reset to return to the initial state.
Frequently asked questions
Is the start day counted?
Yes — the start date counts as day one, the usual way anniversaries are counted.
Can I use it for a work anniversary?
Yes, any start date works — a job, a move, a first meeting.
Which dates are shown?
The 100th, 200th, 300th, 365th, 500th and 1000th days from your start date.