Which Time Is Better for Our Health: Daylight Saving Time or Standard Time?

Most people agree that changing the clocks twice a year is frustrating. The harder question is what we should do instead.

Should we keep daylight saving time all year, giving us more evening light? Should we adopt permanent standard time, giving us more morning light? Or should we continue changing the clocks but divide the year more evenly between the two?

Bottom line: A six-month split may be better than the current schedule, but from a sleep and health perspective, permanent standard time is the best option. It eliminates clock changes and keeps our body clocks more closely aligned with natural light.

Daylight saving time and standard time pull our clocks, and our bodies, in different directions.

What is the difference?

Standard time is the time we currently use during the winter. It is more closely aligned with the natural position of the sun.

Daylight saving time moves the clock forward by one hour. It does not create additional daylight. It simply changes the time shown on the clock when sunrise and sunset occur.

For example, imagine that under standard time the sun rises at 7:00 a.m. and sets at 5:00 p.m. Under daylight saving time, that same sunrise would be labeled 8:00 a.m. and that same sunset would be labeled 6:00 p.m.

We gain an hour of evening light according to the clock, but we give up an hour of morning light. The total amount of daylight remains exactly the same.

Why not continue changing the clocks?

The current system tries to provide later sunsets during the warmer months without forcing us to endure extremely late sunrises throughout the winter.

The problem is that our bodies cannot change their clocks as quickly as our phones can.

The brain’s internal clock, known as the circadian rhythm, is strongly influenced by light. When we move the clocks forward in March, we lose an hour of sleep and suddenly receive less light in the morning and more light in the evening.

Studies have associated the days following the spring change with sleep disruption and short-term increases in cardiovascular events, workplace injuries, medical errors, and motor-vehicle crashes. The strength of these associations varies among studies, but the overall evidence supports eliminating the twice-yearly change.

What about six months of each?

Another possibility would be to continue changing the clocks but divide the year more evenly.

The current schedule is not an even split. Daylight saving time lasts 238 days, from the second Sunday in March until the first Sunday in November. That means we spend about eight months on daylight saving time and only four months on standard time.

A six-month schedule would be a reasonable compromise. We could preserve later sunsets during the summer while avoiding some of the particularly dark mornings in March and late October.

This would not be a new idea. The original schedule established by the Uniform Time Act of 1966 ran from the last Sunday in April until the last Sunday in October, roughly six months.

However, shortening daylight saving time would not eliminate the twice-yearly clock changes or the short-term sleep and health effects associated with them. We would also continue spending half the year on a clock that is less aligned with our natural circadian rhythms.

Six months of each may therefore be better than the current eight-month daylight-saving schedule, but it would still not fully solve the problem.

The case for permanent daylight saving time

Permanent daylight saving time is often the most popular option because people enjoy later sunsets.

More evening light can provide additional time for sports, exercise, shopping, dining, and outdoor activities after work or school. Some research suggests that evening daylight may modestly increase children’s physical activity and reduce certain crimes around dusk. Businesses connected to recreation, retail, and restaurants may also benefit.

Permanent daylight saving time would also eliminate the disruptive clock changes.

The disadvantages become more apparent during the winter. The later sunset comes at the cost of a later sunrise.

In many parts of the country, the sun would not rise until after 8:00 a.m. for weeks or months. Some communities would experience sunrise after 9:00 a.m. Children would travel to school in darkness, and many adults would begin their workday before sunrise.

Morning light is one of the most important signals for setting the body’s internal clock. It helps us become alert earlier and makes it easier to grow sleepy at an appropriate time that evening. Later evening light has the opposite effect and can push sleep later.

Teenagers may be especially affected because their biological clocks already tend to run late. More evening light can make it even harder for them to fall asleep, while school still requires them to wake early.

The United States experimented with year-round daylight saving time in 1974. The plan was initially popular, but support fell once people experienced dark winter mornings. Congress ended the experiment early.

The case for permanent standard time

Permanent standard time would keep the clock we currently use during the winter. We would no longer move the clocks forward in March.

Its main advantage is that it places morning light, noon, and evening darkness closer to their natural solar timing.

That alignment matters because light does more than help us see. It tells the brain when to become alert and when to prepare for sleep. Morning light generally shifts the body clock earlier, while evening light shifts it later.

Permanent standard time would not solve every sleep problem. School schedules, work hours, artificial lighting, screen use, and individual habits would still matter. However, it would give our bodies a more helpful light signal, particularly in the morning.

A 2025 Stanford study modeled the effects of permanent standard time, permanent daylight saving time, and the current system of changing clocks. The model predicted that either permanent option would be better for circadian health than the current system, but permanent standard time produced the greatest benefit.

The researchers estimated that permanent standard time could be associated with 2.6 million fewer people living with obesity and approximately 300,000 fewer people having experienced a stroke. These are estimates from a mathematical model, not the results of an actual nationwide policy change, so they should be interpreted cautiously.

The American Academy of Sleep Medicine, American Medical Association, National Sleep Foundation, and several other scientific organizations support permanent standard time.

Its disadvantage is straightforward: Summer sunsets would occur an hour earlier by the clock.

That could mean less daylight for outdoor activities after work, reduced evening business activity, and very early summer sunrises when many people are still asleep. People who love long summer evenings would understandably feel that they were giving something up.

Which should we choose?

There is no perfect clock policy. We cannot make winter days longer or add more sunlight. We can only decide whether to place more of that light in the morning or evening.

A six-month schedule would be a more balanced compromise than the current system. Permanent daylight saving time may be better for evening recreation, shopping, and dining. It is easy to understand why many people prefer either of those options.

Permanent standard time, however, is better aligned with human circadian biology. It provides more morning light, avoids the latest winter sunrises, and eliminates the disruption of changing the clocks.

The scientific evidence is not perfect, and changing the clock will not fix every sleep or health problem. Still, the evidence consistently points to the importance of morning light and the disadvantages of pushing our schedules later.

My conclusion is the same as that of the American Academy of Sleep Medicine: From a health perspective, we should stop changing the clocks and adopt permanent standard time.

Later summer sunsets may be enjoyable, but when we consider the entire year, our clocks should work with our bodies rather than against them.

Further reading and listening

• American Academy of Sleep Medicine: Permanent standard time is the optimal choice for health and safety

• Stanford Medicine: Comparing permanent standard time, permanent daylight saving time, and seasonal clock changes

• AASM Talking Sleep: Daylight Saving Time: Advocating for Sleep Medicine