Why Am I So Tired in the Winter? The Body Clock Reasons and What Helps

If you're asking why you're so tired in the winter, the main answer is light. Sunrise comes later, most of the day is spent indoors under dim light, and your body clock gets a weaker "it's morning" signal, so your alarm often goes off while your body still thinks it's night. Colds and flu, which peak in the colder months, add to it.

The fix is mostly about the morning: a steady wake-up time and bright light soon after it. To set a bedtime that matches your alarm, start with the sleep calculator.

Why am I so tired in the winter?

Your body clock runs on light, and winter gives it less of it, later in the day. That mismatch makes mornings feel harder and afternoons heavier.

Three things stack up:

• Later sunrise. In much of the US, sunrise in December comes well after many people's alarms. Waking in the dark means your clock hasn't had its main daily reset yet.
• Dim days indoors. Cold weather keeps you inside, and indoor lighting is far dimmer than daylight, even on an overcast day. Your clock gets a weak signal all day.
• Bright evenings. Lamps and screens after dark push your clock later, the opposite of what you need.

A study from the University of Colorado showed how strong this effect is. After a week of camping in natural winter light with no electric lighting, people's biological night began earlier and their sleep started earlier than in their usual modern environment. Their biological night also stretched longer in winter than it did in summer. The researchers found that modern lighting keeps body clocks later in both seasons.

Do you need more sleep in winter?

Possibly a little, but the evidence is limited, and most adults still do well on 7 to 9 hours. There's no official winter guideline.

What research does suggest is that sleep shifts with the seasons. In a Berlin sleep clinic, patients who slept without alarm clocks were measured across a year. Total sleep ran up to about 60 minutes longer in winter than summer, though that difference wasn't statistically clear. REM sleep was about 30 minutes longer in winter than in spring. These were patients with sleep problems in a city, so the results may not apply to everyone.

A practical takeaway: if you feel the pull to sleep more in winter, giving yourself an extra 15 to 30 minutes is reasonable. Here's what that looks like, with 15 minutes to fall asleep included:

Earlier bedtime, same alarm. Sleeping later in the morning instead tends to push your clock later still.

Is it normal to feel tired in winter, or is something wrong?

Some extra sluggishness in winter is common, but feeling exhausted no matter how much you sleep is not something to ignore.

Winter is also cold and flu season, and fighting off an infection makes you tired even before you feel sick. If you are ill, rest helps; how much sleep you need when you're sick covers that.

For some people, winter brings more than low energy. Seasonal affective disorder is a type of depression that usually starts in late fall or early winter and lifts in spring and summer, according to the National Institute of Mental Health. If you feel low most days, lose interest in things you enjoy, or your sleep and appetite change a lot, see a doctor. The same goes for loud snoring, gasping at night, or sleepiness that makes driving unsafe.

How do I stop being tired in the winter?

Fix your wake-up time and get bright light as soon after it as you can. Those two habits do most of the work.

1. Keep the same wake-up time every day. Weekend lie-ins in winter make Monday mornings in the dark harder.
2. Get outside in the first hour after waking. Even a gray winter morning outdoors is much brighter than your kitchen. If it's still dark when you wake, go out at the first chance, such as your commute or a mid-morning walk.
3. Sit by a window for breakfast or work, and turn on bright overhead lights in the morning.
4. Dim the lights in the evening. Lamps instead of overheads, and screens down in the last hour.
5. Watch the afternoon coffee. A slump at 3 PM is tempting to fight with caffeine, but it can still be in your system at bedtime. Check your cutoff with the caffeine calculator.
6. Move during the day, ideally outdoors.

Our guide to waking up at 6 AM goes further on using morning light to make an early alarm feel normal.

Does the end of daylight saving time make winter tiredness worse?

It can for a few days, and then it usually helps your mornings. When clocks fall back, sunrise moves an hour earlier on the clock, so more people get daylight before or during their commute.

The rough part is the first week, when your body still wakes an hour "early" and evenings get dark sooner. Fall back 2026 has the dates and a short plan, and the daylight saving time sleep planner builds a day-by-day schedule from your own bedtime.

What winter tiredness is not

It isn't a sign you need to hibernate or sleep in. Long weekend lie-ins and long afternoon naps can feel good, but they tend to push your body clock later and make the next morning harder.

• Keep naps to about 20 minutes, and before mid-afternoon.
• Don't sleep in more than an hour past your usual alarm.
• If you're sleeping 9 or more hours most nights and still tired, talk to a doctor.