How this calculator works
Completed years are counted the way birthdays are: the anniversary in the reference year either has or has not passed. The next anniversary is the same month and day in the reference year, moved to the following year if it has already passed. Adding whole years before comparing dates is safer than assuming 365 days, because leap years change the gap.
Formula
next = the anniversary date in the reference year, or the following year if its day number is before the reference day. days until = O(next) - O(reference). completed years = reference year - start year, less one when that year's anniversary has not arrived. The milestone label uses the usual English ordinal suffixes, with 11th, 12th and 13th handled separately.
Worked example
An anniversary of 2000-06-15 checked on 2026-11-01 gives 26 completed years. The next anniversary is 2027-06-15, the 27th milestone, and the table lists the dates and weekdays for the next five years.
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Frequently asked questions
Is the first anniversary one year after the wedding or the wedding day itself?
In everyday use the first anniversary is one year after the event, so the completed-year count on the wedding day is zero. The next milestone label shows the anniversary that is still to come.
How is a February 29 anniversary handled?
In a common year it is observed on February 28, matching the convention used for leap-day birthdays. Some records use March 1 instead; the one or two-day difference would then move the count.
Does this include the time of day?
No. It is a whole-date calculation. Two dates are compared as calendar days, so the anniversary is reached at the start of the date rather than at the exact time of the original event.
Can I use it for a work anniversary or a sobriety date?
Yes. Any date being counted from works the same way. For sobriety chips the common convention counts whole days as well, so the total day count matters more than the years alone.