A year felt enormous when you were ten.
Later in life, the same twelve months can seem to disappear.
The clocks did not change.
Your perception of time did.
Scientists do not have one single formula that explains the effect, but memory, attention, novelty, and simple proportion all appear to matter.
New experiences create more memory landmarks
Childhood is full of firsts.
First school.
First sleepover.
First trip somewhere new.
First time learning to drive.
Novel experiences create distinct memories.
When you look back on a period filled with many different events, it can feel rich and long.
Routine creates fewer landmarks.
Why can routine make months blur together?
If Monday looks like Tuesday and this week looks like last week, your memory may store fewer distinctive details.
Looking backward, the period can seem compressed.
This does not mean routine is bad.
It means memory uses noticeable events as markers.
Fewer markers can make a stretch of time feel shorter in hindsight.
One year becomes a smaller fraction of life
For a five-year-old, one year equals 20 percent of everything they have experienced.
For a fifty-year-old, one year equals only 2 percent.
That proportional difference may contribute to the feeling that each year becomes smaller relative to your accumulated life.
It is not a complete explanation, but it is an intuitive part of the experience.
Does time always feel faster while we are living it?
No.
Time perception during an event and time perception afterward can behave differently.
A boring afternoon may feel painfully slow while it is happening.
Months of repetitive afternoons may later feel as though they disappeared.
Attention stretches the moment.
Memory compresses the routine.
Can novelty make life feel slower again?
Novel experiences can create more memory detail.
Learning something new, visiting unfamiliar places, meeting new people, or changing routines can make a period feel more substantial when you look back on it.
That does not literally slow time.
It gives memory more material.
Why does age matter if routine is the real problem?
Age often brings more repeated patterns.
Work, errands, household routines, and familiar environments can make days resemble one another.
That is not universal, but it is common enough to influence time perception.
So time itself is not getting faster.
We are changing how much detail we notice and remember along the way.
Which is still pretty rude of time.
A related piece of human behavior appears in Why do we get déjà vu?, where the brain handles another everyday judgment or response.
And that’s the short explanation.
Related explanations: Why do we get déjà vu?, Why do unfinished tasks stay in your mind?, and Why do we forget dreams so quickly?