Know when to focus, rest and sleep.

Your circadian rhythm is your body’s roughly 24-hour clock. Together with sleep pressure, the need for sleep that builds the longer you’re awake, it shapes when you tend to feel alert and when you tend to feel tired.

Many people feel a strong stretch in the morning, a dip in the early afternoon, a second wind later in the day and a natural slowdown in the evening. The exact timing differs from person to person.

Light is the main signal that keeps this clock on time. Daylight in the morning helps set it, while bright light late in the evening can push it later.

Rhythm draws your day as an arc from 6 am to midnight and splits it into parts you can feel:

• Morning rise and Morning peak. You come out of sleep, then often reach your clearest hours.
• Post-lunch dip. A natural lull in the early afternoon, often stronger after a short night.
• Second energy peak. A lift later in the afternoon.
• Evening descent. Things start to slow down toward bedtime.
• Sleep Gate and your sleep window. Your best time to go to bed, and the night that follows.

Tap Now to read about the part of the day you’re in, or drag along the arc to look ahead. The arc is anchored to when you actually wake up and go to sleep. Without sleep data, Rhythm shows a general curve; with it, the timing becomes yours.

With Apple Weather connected, today’s real sunrise appears on the arc, and tips can take rain, snow or cold into account.

Your chronotype is your natural timing: whether your body leans toward early mornings, late evenings or somewhere in between. Wonderwake finds it from when the middle of your sleep usually falls across recent nights.

After about five nights of sleep data, from Apple Health or just your iPhone, your chronotype is ready and you reveal it with one tap. If your sleep timing shifts for a week or more, it can shift with it, but one late night won’t change it.

Each time you open Rhythm, three short cards explain the part of the day you’re in and suggest what might help, like getting daylight in the morning or keeping the evening dim. They take your recent sleep, sleep debt and activity into account.

• Plan the hard stuff for a peak. Save focused work for your morning peak or second energy peak.
• Go easy during the dip. Lighter tasks, a walk outside or a short nap fit the early afternoon.
• Wind down on time. Dimmer light and fewer screens as you approach Sleep Gate make it easier to fall asleep.

Rhythm is a guide to likely peaks and dips, not a measurement of your energy.