What this set is
The same day counts as days from today, run backwards. Each page gives the exact date, the weekday it fell on, the ISO week, the business-day equivalent, and any holiday or clock change inside the span.
The intent behind a lookback is different from the intent behind a countdown, and the numbers show it. Forward counts are deadlines; backward counts are records. 30, 60 and 90 days back are statement periods, return windows and billing-dispute rights; 60 days back is the Fair Credit Billing Act window; 180 days back is the outer limit for an EEOC charge in states without a deferral agency; and the longer counts are background-check and tenancy-screening lookbacks.
The counting rule
The start date is not counted here either: "30 days ago" is the date 30 days before today, not the 30th day of a run ending today. Both figures are shown on every page. If you need the span between two specific dates rather than a count back from today, the days between dates tool is the right one — it also shows the inclusive count, which is what a hire period or a hotel stay usually means.