Tool
Anniversary Across Timezones
Track a multi-city anniversary (work, relationship, founding date) and see which city marks each year-milestone first.
What makes this different
The milestone view (1, 5, 10, 25 years) is what makes this different from the birthday tool. Anniversaries compound, and the order can shift across the decades as countries add or drop DST.
How to use it
- Pick the anniversary date.
- Pick the cities.
- Read the milestone calendar: each city's first-to-celebrate status for year 1, 5, 10, 25.
Anniversaries, like birthdays, are anchored to a date. When the date is meaningful to people in several cities, the question of which city reaches the anniversary first matters: it is usually the city that hosts the founder or the spouse. This tool computes the order across years for a chosen list of cities, and surfaces the 1, 5, 10 and 25-year milestones.
Frequently asked questions
Why does the first city change with the year?
Because DST shifts change offsets, sometimes enough to swap two cities. This is rare for adjacent-year anniversaries but accumulates over decades.
What if the anniversary is February 29?
Treated as March 1 in non-leap years. Most anniversary-tracking systems use this convention.
Can I add custom milestones?
Not in the current version. The four fixed milestones (1, 5, 10, 25) cover the common cases for product and personal anniversaries.