Days Since / Milestone Calculator
How it works
Today's date and the start date are both anchored to UTC midnight, and the count is simply the whole number of days between them — negative when the start date is still ahead of today. That same day count is then compared against a fixed list of round numbers (100, 500, 1000, 2000, 5000, 10000) to find the smallest one still in the future, and its calendar date is worked out by adding that many days back onto the start date.
Frequently asked questions
What does a negative "days since" mean?
That the start date has not happened yet — it is in the future relative to today. Rather than treating that as an error, the tool doubles as a countdown: a negative days-since is exactly how many days remain until the date arrives.
What does the milestone list cover, and can I change it?
It is a fixed set of round numbers most people find meaningful — 100 days, 500, 1,000, 2,000, 5,000 and 10,000 — rather than a customizable list. Keeping it fixed keeps the tool simple: one headline, always the next round number worth marking, with nothing to configure first.
How is this different from the Age Calculator?
The Age Calculator is specifically about a birth date, and reports age broken into years, months and days. This tool works from any start date at all — a relationship anniversary, a quit date, a first day at a job — and instead of a calendar breakdown it counts total days and highlights the next round-number milestone.