Time seems to speed up with age because adult life holds fewer new experiences. The brain stores novel moments in rich detail and compresses routine ones. A year packed with firsts feels long in memory. A year of repeated days leaves little behind, so it seems to have flown.

Remember being ten? The summer holidays stretched out like a small lifetime. Now you blink in January and someone is hanging festive lights again. The calendar hasn't changed. You have.

The maths of a shrinking year

One of the oldest explanations comes from the French philosopher Paul Janet, writing in the 1870s. He pointed out that we judge a stretch of time against the life we have already lived. For a ten-year-old, one year is a tenth of everything they have ever known. For a fifty-year-old, it is a mere fiftieth.

It's a neat idea, and it feels true. But it doesn't explain why a single eventful week can feel longer than a quiet month. For that, we need to look at memory.

Your brain keeps the firsts and bins the repeats

Childhood is a parade of firsts. First bicycle, first school, first time staying up past midnight. The brain treats new experiences as worth recording, and it records them in detail.

Adult life runs on routine. Same commute, same desk, same Tuesday. Your brain, being efficient, stops taking detailed notes. When you look back on those months, there are fewer distinct memories to count. Less footage means the period feels shorter.

The writer Claudia Hammond calls a related effect the holiday paradox. A week away races past while you're in it. Yet when you return, it feels as if you've been gone for ages, because you packed so many new memories into seven days.

Is the brain itself slowing down?

There may be a physical side too. Duke University professor Adrian Bejan has proposed that ageing brains process mental images more slowly. Fewer new images per second of clock time would make each day feel like it holds less. It remains a hypothesis, but it fits the lived experience rather well.

Five ways to make time feel longer

You can't add hours to the day. You can add memories to it.

1. Break one routine a week. Take a new route, cook an unfamiliar dish, sit in a different chair. Small changes still register as new.
2. Learn something hard. A language, an instrument, a sport. Being a beginner forces your brain to pay attention again.
3. Travel, even locally. A day trip to a town you've never visited does more for your sense of time than a weekend on the sofa.
4. Put the phone down. Scrolling eats hours and leaves almost no memories behind.
5. Keep a one-line journal. Writing a single sentence each night gives every day its own marker.

The takeaway

Time doesn't speed up. Our days simply start to look alike, and the brain files them as one. Fill the year with a few more firsts and it will feel, in hindsight, a good deal longer.