Quick Answer: Three things stack up. You have spent months in near-weightless clothing, so a 1.5kg coat is a large relative change your body has no recent reference for. Your thermal acclimatisation is still set to summer, so 14 degrees feels colder than the same temperature will in March and warmer than you dressed for. And September temperatures swing 10 degrees across a day, so the coat that was right at 8am is genuinely surplus by 2pm. By January none of the three applies.

You took the coat out on the first properly cool morning and it felt like putting on armour.

In January you will wear the same coat over a jumper and barely register it.

Why does the weight itself feel so different?

Relative change is what your body notices, not absolute weight. After a summer of 200-gram outfits, a 1.5kg coat is a very large proportional increase.

Weight sits on the shoulders, which is a sensitive area with no recent load and produces immediate awareness.

Sleeves add resistance to arm movement, and a lined wool sleeve is genuinely more work to move through than a bare arm.

Habituation is fast but not instant. Within about two weeks of regular wear the same coat stops registering, which is exactly what has happened by January.

Layers underneath change the sensation too. A coat over a summer top sits directly on the shoulders; a coat over a jumper distributes across a padded surface and reads as lighter.

And carrying is separate from wearing. In September you take the coat off and carry it half the day, which genuinely is heavy - in January it stays on.

How much of it is thermal acclimatisation?

Substantial, and it is a real physiological process. Your body adapts to a temperature range over weeks, and after a summer that range is set high.

Fourteen degrees in September is the coldest thing you have felt in months and the same 14 degrees in March is a genuine relief - the temperature has not changed and you have.

Blood flow patterns adjust seasonally, which is why extremities feel the cold more acutely early in the season.

The adaptation takes roughly two to three weeks of exposure, which maps precisely onto the period where autumn dressing feels most confusing.

Which means you over-dress in September and under-dress in March at identical temperatures, and almost everyone does it.

And the coat is caught in the middle of that, feeling excessive at a temperature that will feel coat-appropriate six weeks later.

What about the daily temperature swing?

September commonly swings 10 degrees or more between morning and mid-afternoon, which is a wider range than any single garment handles.

January swings much less, typically 4 to 6 degrees, so one coat is genuinely correct all day.

Which makes September a layering problem rather than a coat problem, and reaching for the coat is often the wrong first move.

A mid-weight jacket plus a knit outperforms a heavy coat across an autumn day, because you can remove one of the two.

Morning is the trap. Dressing for 8am on a September morning reliably over-dresses you for the following six hours.

And the answer is to dress for the afternoon and carry one thing for the morning, which is the inverse of what most people instinctively do.

5 Early-Autumn Coat Mistakes

1. Bringing out the heavy coat on the first cool morning. The first genuinely cool morning arrives well before coat weather does. It is a mid-weight jacket moment, and the heavy coat brought out too early spends the season being carried rather than worn.

2. Buying a coat in early September based on how it feels. Your acclimatisation is at its summer setting, so every coat feels warmer than it will in November. This is precisely why people buy coats that turn out to be too light for actual winter - the shop trial was conducted on an unrepresentative body.

3. Dressing for the morning temperature. The morning is the coldest 90 minutes of a September day and you will spend six hours in something warmer. Dressing for the afternoon and carrying one extra layer is the correct order.

4. Skipping the mid-weight layer entirely. A great many wardrobes go straight from summer jacket to winter coat, leaving a six-week gap at each end of the year that gets solved badly. The mid-weight jacket is the single most useful autumn purchase and the one most often skipped.

5. Judging the coat by the first wear. Everything feels heavy and unfamiliar the first time after months away. Give it three or four wearings before deciding it is wrong, because habituation genuinely resolves most of the objection.

And the bonus: forgetting that the coat needs to work over your actual autumn clothes. A coat tried on over a summer top in August will be tight over a chunky knit in November, and the shoulder is where it fails first. Take a jumper to the fitting room.

FAQ: Autumn Coat Questions, Answered

When should I actually start wearing a coat?

When the afternoon temperature, not the morning one, sits in coat range. For most people that is several weeks after the first cool morning.

Why does the coat feel fine by October?

Habituation to the weight takes about two weeks of regular wear, and thermal acclimatisation takes two to three. Both have happened by then.

Should I buy a coat in August sales?

The prices are good and your judgement is not - you are acclimatised to summer. Try it over a jumper and trust the weight and construction more than how warm it feels.

What is the most useful autumn outer layer?

A mid-weight jacket you can wear over a knit. It covers the six-week gap at both ends of winter that most wardrobes handle badly.

Why do I feel colder in September than in March at the same temperature?

Seasonal acclimatisation. Your body’s comfort range is set by recent exposure, and in September that setting is still summer.

How do I stop carrying my coat all afternoon?

Wear layers instead of one heavy piece. A knit you can push into a bag is far easier to carry than a wool coat over your arm.

TL;DR:

• After a summer of near-weightless clothing, a 1.5kg coat is a large relative change your body has no recent reference for.
• Thermal acclimatisation is still set to summer, so September’s 14 degrees feels colder than March’s identical 14 degrees.
• September swings 10 degrees across a day; January swings half that, which is why one coat works then and not now.
• Dress for the afternoon and carry one layer for the morning, rather than the reverse.
• A mid-weight jacket over a knit beats a heavy coat for the whole transition, and it is the most-skipped autumn purchase.

The coat did not get heavier. You spent three months in nothing at all.