Date Ranges in Criteria Functions

Real reports almost always ask about a time window: sales this quarter, orders last month, signups between two dates. The criteria functions you've learned — SUMIFS, COUNTIFS, AVERAGEIFS — handle this beautifully once you know how to express a date range.

The trick is that a date range is really two conditions on the same date column: on or after a start, and on or before an end.

Spreadsheets store dates as serial numbers — day 1 is January 1, 1900 (or 1899 in Sheets), and each later day adds one. That's why you can compare dates with > and < exactly like ordinary numbers.

So after January 1 simply means a serial number greater than that date's number. This is the key insight that makes date filtering work.