What Was the Date 100 Days Ago?
The date 100 days ago was:
Which Day Counts as Day One?
Counting backwards has the same off-by-one ambiguity as counting forwards. Both readings are shown here so you can match the wording of whatever rule, form, or policy you are working with.
Yesterday = day 1 (the usual rule)
May 15, 2026
Today is day 0; count 100 full days back. This is the main answer above.
Today = day 1 (inclusive counting)
May 16, 2026
Some rules count today as the first of the 100 days, landing one day later.
Is a Date Within the Last 100 Days?
Pick the date on your receipt, statement, or record and see exactly how many days back it falls — and whether it is still inside a 100-day window.
What 100 Days Ago Means
The round-number milestone, looking back
One hundred days ago is a milestone date more than a deadline date. People look it up to date the start of a streak or challenge, to mark 100 days since a launch, a loss, or a change, and to write retrospectives that begin "100 days ago today."
Because 100 is not divisible by 7, the weekday shifts relative to today — 100 days back is 14 weeks and 2 days, so it lands two weekdays earlier in the week than today.
Common Reasons to Look Back 100 Days
- Dating the start of a 100-day streak, challenge, or program
- Writing a "first 100 days" retrospective for a role or project
- Marking 100 days since a launch, move, or life event
Why 100 Days Became the Standard Retrospective Length
The "first 100 days" framing dates back to Franklin D. Roosevelt’s first months in office in 1933, and it stuck because 100 days is long enough for real change to show while still feeling like a beginning. Today it is applied to new executives, new products, and personal goals alike.
For habit tracking, the round number does real work: streak apps and challenges use 100 days because it is memorable and just over three months — past the point where most habits either stick or quietly die.
- The framing traces to FDR’s first 100 days in 1933
- 100 days ≈ 14 weeks and 2 days — the weekday shifts by two
- Long enough to judge a habit, short enough to feel fresh
How This Calculation Works
This page counts exactly 100 calendar days backwards from today — weekends and holidays included — using your local date, so the answer rolls forward at your local midnight. The calendar below marks every day in the lookback span so you can trace it against month boundaries. Planning forwards instead? See 100 days from today. If your rule counts working days only, use the business days calculator, and for arbitrary numbers or specific start dates, the main days calculator handles both directions.
Calendar View
Additional Information
Explore Other Lookbacks
Frequently Asked Questions
Count back 100 calendar days from today's local date, treating yesterday as 1 day ago — so today itself is day 0. Saturdays, Sundays, and public holidays are all included. Because the count starts from your local "today," the answer rolls forward at your local midnight.
Under the usual convention, no: today is day 0 and yesterday is day 1, which is the main answer shown on this page. Some rules count inclusively instead, treating today as day 1 — that reading lands one day later, and both dates are shown side by side above so you can match the wording of your rule.
Usually yes — "within the last 100 days" almost always means the window from that date through today, inclusive at both ends. The date shown above is the oldest date that still qualifies; anything earlier falls outside. Use the window checker on this page to test any specific date.
Yes. This page counts calendar days, so every day on the calendar is included. If your rule counts working days instead — "10 business days" is a different span than 10 calendar days — use the business days calculator.