Index / Time
As Long Ago As
Pick a date. This works out the date that was the same distance before it as it is before today — the sentence that makes everyone feel old — and then keeps going, one equal step at a time.
The date
1997 and 1997-05-21 are both read. A year on its
own is taken as the first of January.
Today, unless you change it.
Just as long ago
--
The gap
--
In days
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The ladder
The gap, measured every way
and the same distance forwards
Two ways to mirror a date, and they do not agree
By days. Count the days from the date to today, then count the
same number of days back again. This is exact, it needs no conventions,
and it is what the headline uses. Over a long gap it drifts away from the
calendar answer, because the number of days in a year is not constant:
leap days accumulate.
By calendar years. Take the whole number of years between the date and today, and subtract that many years again. This lands on the same day of the month, which is what people mean when they say “1997 was as long ago as 1968”, and it needs the end-of-month rule: one year before 29 February is 28 February, because the day does not exist. Both answers are printed and they differ by a day or two over a long gap.
A year on its own is mirrored in years; a full date is mirrored in days. They are different questions and they give answers a few months apart, so the page picks by what you typed and says which it used. Typing 1997 gives 1968, which is the sentence people mean; typing 1997-05-21 gives an exact date 10,000-odd days earlier.
The ladder takes equal steps. Each rung is the same gap again, so the years come out evenly spaced — 2026, 1997, 1968, 1939 — rather than halving. That is the version of the sentence people find unsettling, which is presumably why it keeps being posted.
Whole years, months and days use the clamping rule. Counting from 31 January, one month later is 28 February, and the count of whole months only increases on the 28th. It is the same rule the age calculator on this site uses, and it is the one place two calculators of this kind routinely disagree.
A year under 100 means that year. JavaScript's date constructor still maps 0 to 99 onto 1900 to 1999, so
Dates are calendar dates, with no time and no zone. Nothing here involves an hour, so nothing here can be off by one from a time zone. The Gregorian calendar is projected backwards without limit, which is what every date library does and which is not what happened historically: Britain and its colonies did not adopt it until 1752, and dates before that in local records are eleven days out.
A date in the future is refused rather than mirrored. The whole sentence depends on the date being behind you.
By calendar years. Take the whole number of years between the date and today, and subtract that many years again. This lands on the same day of the month, which is what people mean when they say “1997 was as long ago as 1968”, and it needs the end-of-month rule: one year before 29 February is 28 February, because the day does not exist. Both answers are printed and they differ by a day or two over a long gap.
A year on its own is mirrored in years; a full date is mirrored in days. They are different questions and they give answers a few months apart, so the page picks by what you typed and says which it used. Typing 1997 gives 1968, which is the sentence people mean; typing 1997-05-21 gives an exact date 10,000-odd days earlier.
The ladder takes equal steps. Each rung is the same gap again, so the years come out evenly spaced — 2026, 1997, 1968, 1939 — rather than halving. That is the version of the sentence people find unsettling, which is presumably why it keeps being posted.
Whole years, months and days use the clamping rule. Counting from 31 January, one month later is 28 February, and the count of whole months only increases on the 28th. It is the same rule the age calculator on this site uses, and it is the one place two calculators of this kind routinely disagree.
A year under 100 means that year. JavaScript's date constructor still maps 0 to 99 onto 1900 to 1999, so
new Date(1, 0, 1)
is 1 January 1901. This page undoes that: typing 0050 gives the year 50,
not 1950.
Dates are calendar dates, with no time and no zone. Nothing here involves an hour, so nothing here can be off by one from a time zone. The Gregorian calendar is projected backwards without limit, which is what every date library does and which is not what happened historically: Britain and its colonies did not adopt it until 1752, and dates before that in local records are eleven days out.
A date in the future is refused rather than mirrored. The whole sentence depends on the date being behind you.