Why does time seem to speed up as you get older?
Because you judge elapsed time largely by how much you remember of it, and a familiar year lays down far fewer distinct memories than a novel one.
Simple intuition
The plain reason, in everyday words
There are two different questions hiding here. How long does an hour feel while you are in it, and how long did last year feel once it is over? The second is the one people mean, and the answer seems to be that you judge a past stretch of time by how much of it you can retrieve. A childhood summer contained a great deal that had never happened before — new places, new skills, first times — and each of those laid down a distinct memory, so the season is richly represented and feels long in retrospect. An adult year of familiar work, familiar routes and familiar routines lays down far fewer distinguishable memories, because your brain does not store the ten thousandth commute separately. Less recorded, less to look back on, and the year feels as though it went past in a moment.
Your internal clock literally slows down with age.
Laboratory tests of short-interval timing do not consistently show this. The effect is mainly in retrospective judgement of long periods, which is a memory phenomenon rather than a clock one.
It is because each year is a smaller proportion of your life.
That framing is intuitive but has little direct evidence, and it fails to explain why a novel week feels long in retrospect or why lockdown distorted time for people of all ages.
Time feeling fast and time feeling slow are the same measure.
An interval can drag while it happens and vanish in memory, or fly by and feel long afterwards. Prospective and retrospective judgements are separate and often opposite.
Nothing can be done about it.
If the memory-density account is right, novelty and varied routine increase the number of distinct encoded events, which is the input the judgement is built from. That prediction is testable and broadly supported.
It shows that a subjective experience everyone shares can be well documented and still lack a settled explanation — and that the popular explanation is often the least supported one. It also carries a rare directly usable implication: if how long a period feels depends on how much of it you encoded, then the composition of your routine is the variable you control, and sameness has a specific cost.
Who worked it out
Paul Janet proposed the proportional theory in 1877 — that each interval is judged against the length of life so far — and it has remained the popular explanation ever since despite thin evidence.
What problem forced it
Twentieth-century psychology separated prospective from retrospective timing, which showed that the two behave differently and often oppositely, and that the folk question is about the second.
How it changed since
Survey work has since established the phenomenon across cultures and ages, while the mechanism remains contested between memory-density accounts, processing-rate proposals, and explanations grounded in the reminiscence bump.
Why memories cluster between 10 and 30
The reminiscence bump gives a specific reason that period feels so dense when you look back on it.
How attention shapes duration in the moment
The other half of the question, which works by an entirely different mechanism.
Written for Curio rather than collected from a forum — it is part of the curated corpus that ships with the platform. The references it draws on are listed under Sources.