100 days back — the threshold where new things stop being new.
Type any number to find that date.
A hundred days back is the moment things settle. The new president, new CEO, new coach gets evaluated at this distance — the famous 'first 100 days' that started with FDR in 1933. The Lally et al. UCL study found this is also roughly when new behaviors become automatic for most people.
By day 100, the new is no longer new. The job. The routine. The leadership. Whatever started 100 days ago has either become the way things are or hasn't survived. The number has cultural weight because so many evaluation cycles use it: presidential first-100-days, school 100th-day milestones, 100-day challenges that finished today. The number is also a useful threshold in habit research. UCL's 2009 study found that automaticity for new behaviors stretches from 18 to 254 days, with a median around 66. By 100 days, most habits that survive have become things you don't think about.
New presidents, CEOs, and head coaches are traditionally judged at the 100-day mark. The framework dates to FDR's first 100 days in 1933.
Many US elementary schools mark the 100th day of school with counting projects. The 100th day is roughly 100 calendar days back from late January or early February.
If you started a 100-day commitment 100 days ago, today is the last day. The number has sticking power because it's round and final.
The UCL habit research found new behaviors typically reach automaticity around day 100 for the median person.
The first 100 days of any presidency are now inevitably compared to FDR's 1933 sprint. By June 16 of that year, Congress had passed 15 major bills creating the FDIC, the TVA, the Civilian Conservation Corps, and the framework of the New Deal. Every leader since has been measured against that pace, fairly or not.
Here's the corresponding date for each of the days around today:
| Reference | Reference date | −100 days |
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