How do you compare the same month in different years?

"Was this September anything like last September?" sounds like a question with a real answer sitting somewhere in your head. Try to actually retrieve it and what comes up instead is a mood — this September felt heavier, or easier, or the same as always — standing in for a comparison you never actually made. A month is long enough to have a real shape and short enough that memory almost never keeps that shape intact for two of them at once.

A month is the wrong size for memory to hold twice

A week is short enough that you can sometimes still feel its texture a year later, especially if something notable happened in it. A year is long enough that memory gives up on detail early and hands you a single label instead — "the year we moved," "a good year," "a hard one." A month sits in between, and that in-between size is exactly what makes it so unreliable to compare from memory. It is too long to recall the way you recall a single week, and too short to have earned the kind of one-line summary a year gets. What is usually left, when you try to compare this September to last one, is not two months. It is one vague label for the current one and almost nothing for the other, filled in by guesswork that leans on whatever else you remember about that year in general.

Why the same month across years is a strange comparison to make

Comparing this week to last week at least compares two things you were recently inside of. Comparing this September to last September asks you to reach across a year, past everything that happened in between, and hold two specific slices steady against each other — without the months on either side leaking into the comparison. In practice they leak constantly. If last year's September was followed by a genuinely bad October, September itself tends to get pulled down in memory, tinted by what came right after it even though nothing about September changed. A record does not have this problem, because it was written before it knew what October would bring.

What actually tends to differ between two Septembers

Once you have both months as something other than a mood, the differences worth looking for are rarely dramatic. They are usually quieter than "better" or "worse":

• What the month opens with. A school year starting, a project kicking off, a season turning — the first week of a month often sets a tone that colours how the rest gets remembered, whether or not it holds.
• Who shows up in it. A name that fills half of last September and is nowhere in this one is a more honest signal than any sense of whether the month "felt" different.
• Where the colour sits. If your categories carry a colour, one September leaning almost entirely into one of them next to another with a real mix is visible before you read a single line.
• What routine looks like in each. The same month a year apart can be organized around completely different anchors — a commute that no longer exists, a class that has ended, a habit that started since.

None of this requires a duration attached to any of it. Two entries that both just say "back at the desk by six" carry the comparison on their own.

The trap: comparing a September that had something happen in it to an ordinary one

The comparison that misleads people most is a month with a real event in it — a move, a loss, a new job, a diagnosis — set against an unremarkable one from another year and judged as if they were the same kind of month to begin with. Of course they read differently. They were different on purpose, for reasons that say nothing about whether your life in general has gotten better or worse since. An eventful month is worth keeping and worth rereading. It is not a fair stand-in for what a normal month in that year looked like, and treating it as one usually just tells you what you already knew: that year had that thing happen in it.

What a real pattern looks like once you find one

The differences worth noticing are quieter than a verdict. A category that filled a third of last September and is down to almost nothing this year. A name that used to show up every week in this exact month and has not appeared since spring. A month that has twice as many entries as the same month a year ago, with no single event that explains it. These are not scores. They are observations about how a specific, recurring slice of your year has actually changed shape — which is a different and more useful question than whether this year is going "well" in general.

TimeMap keeps every logged day filed to its date, so pulling up the same month from two different years is a matter of opening both on the calendar rather than trying to hold them in your head at once — categories, colours, and the words you actually used, lined up instead of guessed at. It will not tell you which September was the better one. It will show you what each one actually contained, which turns out to be the more useful thing to know.

The next time "was this September like last one" comes up, it is worth noticing that the honest answer is not available yet from memory alone — and that the question was always answerable, just not from where you were standing when you asked it.