What it recognizes
Anything with the year in front is unambiguous and is read as written: 2026-03-05, 2026/3/5, 2026.3.5. Eight solid digits, 20260305, are read as year-month-day, but only when no other digit is touching them, so an order number or a phone number does not get mistaken for a date. Month names work in both orders, Mar 5, 2026 and 5 March 2026, spelled out or abbreviated, with or without an ordinal suffix. Two-digit years are refused. 26-3-5 could be 1926 or 2026, and quietly assuming the 2000s is how a date of birth ends up a century out. If you know every row is in this century, prepend 20 with the find and replace tool first.
The 3/5/2026 problem
Three numbers separated by slashes are read two different ways in different parts of the world. The United States writes month first, most of Europe and Australia write day first, so 3/5/2026 is March 5 to one reader and May 3 to another. Rather than guess, this asks you which order the data was written in and defaults to the US reading. It only asks when it has to: if either number is over 12 there is only one possible reading, so 25/3/2026 comes out as March 25 whichever order you picked. Every line where the choice actually mattered is tagged "order applied" in the results table, which turns the problem into a short list to eyeball rather than a whole column. If you genuinely do not know the source, set the order to leave them alone and read the count first — knowing there are four such rows out of six hundred is a different problem from knowing there are four hundred.
Impossible dates do not get through
Most software takes 02/30/2026 and hands back March 2, because the underlying date object adds the overflow onto the next month. A single typo becomes a wrong-by-two-days value that looks perfectly ordinary from then on. Here the date is built and then read back: if the year, month or day that comes out is not the one that went in, the line is rejected and the reason is printed next to it. February gets the leap year worked out as well, so 02/29/2026 is refused as a common year and 02/29/2028 is accepted. The leap rule is every year divisible by 4, except years divisible by 100, except again years divisible by 400 — which is why 2000 was a leap year and 1900 and 2100 are not.
Keeping the rest of the line
With the keep-the-rest option on, only the first date-shaped run in a line is replaced and everything around it is left untouched, so 2026-03-06 deposit due becomes 03/06/2026 deposit due. A line holding two dates only has its first one rewritten. A range such as 3/5/2026 - 3/9/2026 will therefore come out half converted; split those on the dash into two lines before pasting, being careful that ISO dates contain dashes of their own. Turn the option off and the output is a bare column of dates, ready to paste into a spreadsheet — at the cost of losing lines that had no date on them, so the row count no longer matches the source.
Questions people ask
Can I paste a column straight out of a spreadsheet?
Yes. Copying a single column puts one cell per line, which is the shape this expects. What you get is whatever the cells were displaying, not what they hold underneath, so a cell already formatted as a date arrives in that display format. When pasting the result back, set the destination column format first — especially for the 20260305 form, which a spreadsheet will read as a number.
Why will it not read a two-digit year?
Because the century is unrecoverable. For a contract date 26 almost certainly means 2026; for a date of birth it may well mean 1926. Different programs pick different cutoff years, so the same file read in two places produces two different dates. Those lines are counted as having no date rather than being guessed at.
How is the weekday worked out?
The date is constructed from separate year, month and day numbers at local midnight, and the weekday is read off that. Parsing an ISO string instead would produce a UTC instant, which lands on the previous day for anyone west of Greenwich and shifts the weekday with it. Dates before the Gregorian calendar was adopted in 1582 are extrapolated backwards by the browser and will not match historical records.