How Much Vitamin D Can You Get From The Sun? The Numbers

Sunlight is the main natural source of vitamin D for most people, and the amount your skin can make depends on where you live, the season, the time of day, your skin tone, and how much skin you expose. Under strong summer sun, a fair-skinned person exposing most of their body may produce the equivalent of roughly 10,000 to 25,000 international units (IU) of vitamin D in a single session before the skin begins to break down the vitamin. For darker skin, older adults, and anyone in northern latitudes during winter, that number can drop sharply — sometimes to nearly zero.

Those figures are estimates from research, not a dose you can measure off a chart. There is no universal number that applies to everyone, because the skin’s vitamin D production is a moving target. What follows is what the science actually shows about the numbers, and where the limits are.

How Much Vitamin D Can You Get From the Sun?

There is no fixed amount. The skin’s output depends on ultraviolet B (UVB) radiation reaching the skin, and that varies enormously by person and by moment.

Researchers have estimated that a single exposure of most of the body to one minimal erythemal dose (MED) — the amount of sun that turns skin slightly pink about 24 hours later — produces roughly 10,000 to 25,000 IU of vitamin D in lighter-skinned people. That estimate comes from controlled studies and modeling, and it is widely cited. It is not a target. It describes what the skin can do under near-ideal conditions, not what most people actually get.

The reason the range is so wide is that MED itself varies. It might take 15 minutes of midday summer sun to reach one MED in a fair-skinned person, while a person with deeply pigmented skin may need several times longer to reach the same threshold. The same sun, the same hour, produces very different vitamin D totals in two different people.

Two more points matter. First, once you have reached your MED, additional sun does not keep adding vitamin D. The skin reaches a plateau and then begins converting the vitamin D it made into inactive forms. More sun is not more vitamin D — it is more skin damage. Second, the body regulates this process, which is why sun exposure does not cause vitamin D toxicity. Oral supplements can, in extreme doses, but the skin’s own production is self-limiting.

What Factors Change How Much Vitamin D You Make?

Several factors decide whether your skin makes vitamin D at all on a given day, and how much.

• Latitude and season: Above roughly 35 degrees latitude — which includes most of the continental United States in winter — the sun’s angle is too low for enough UVB to reach the ground. From about November through February, skin in these regions makes little to no vitamin D, no matter how long you stay outside.
• Time of day: UVB is strongest near solar noon, roughly between 10 a.m. and 3 p.m. in most of the US. Early morning and late afternoon sun is largely UVB-free.
• Skin tone: Melanin absorbs UVB. More melanin means slower vitamin D production and a longer time to reach the same output. People with darker skin often need significantly more sun exposure to make the same amount.
• Age: The skin’s ability to synthesize vitamin D declines with age. Older adults make less from the same sun exposure.
• Skin exposed: A face and hands make far less than arms, legs, and back. The more skin uncovered, the more vitamin D.
• Sunscreen: Sunscreen blocks UVB, which is the same wavelength the skin uses to make vitamin D. In real-world use, people rarely apply enough sunscreen to block production completely, so the practical effect is smaller than lab tests suggest. But heavy, correct use does reduce vitamin D synthesis.
• Air pollution, glass, and cloud cover: Glass blocks UVB almost entirely, so sun through a window makes no vitamin D. Pollution and dense cloud can also reduce UVB reaching the skin.

How Long Do You Need to Stay in the Sun?

For a fair-skinned person in strong midday summer sun, 10 to 20 minutes on exposed arms and legs is often enough to reach one MED and trigger substantial vitamin D production. For darker-skinned people, older adults, or anyone in weaker sun, the time needed can be much longer — or the skin may never reach that threshold before the sun sets or the season changes.

The commonly cited guidance is to spend about half the time it would take your skin to burn, then get out of the sun. This is a general principle, not a precise formula, and it depends on knowing your own skin. The point of stopping early is that vitamin D production is already near its peak by the time skin starts to turn pink.

What this guidance does not mean is that you should tan or burn. There is no evidence that a tan is a sign of healthy vitamin D levels, and tanning is a known risk factor for skin cancer. The goal, if you choose sun exposure for vitamin D, is brief and moderate — not prolonged.

Can You Make Vitamin D in Winter or Through a Window?

In most of the US, no — not in winter, and not through glass.

During winter at higher latitudes, the sun’s UVB is filtered out by the atmosphere. Even on a clear, bright day, the skin makes little or no vitamin D. This is why blood levels of vitamin D commonly fall in late winter. People in northern states, and anyone who spends most daylight hours indoors, are the most affected.

Window glass blocks nearly all UVB. Sitting in a sunny window, even for hours, will not raise your vitamin D. It may feel warm, and it may expose you to UVA, but UVA does not make vitamin D. It does contribute to skin aging.

Cloud cover reduces UVB but does not eliminate it. A partly cloudy summer day can still support vitamin D production. A heavily overcast winter day at high latitude usually cannot.

What Are Normal Vitamin D Levels?

Blood levels of 25-hydroxyvitamin D — the form doctors measure — are the standard way to know your vitamin D status. The most widely used threshold for sufficiency is 20 ng/mL (50 nmol/L) or higher. Some organizations and researchers argue for 30 ng/mL, but that higher cutoff is debated.

For context:

• Deficiency is generally defined as below 20 ng/mL (50 nmol/L).
• Insufficiency is often described as 20 to 29 ng/mL.
• Sufficiency is commonly set at 20 ng/mL or above.
• Excess is generally considered above 100 ng/mL.

These are established reference points used in clinical practice. They are not a reason to guess at your own level. The only way to know your vitamin D status is a blood test ordered by a clinician.

Is Sun Exposure Enough to Meet Your Vitamin D Needs?

For some people, in some seasons, sun exposure can maintain adequate vitamin D. For many others, it cannot — and the evidence does not support relying on the sun alone as a reliable strategy.

The problem is that the factors above are not within your control. Latitude, season, skin tone, and age all limit how much vitamin D your skin can make. A person in Minnesota in January, or a person with deeply pigmented skin living in a northern city, may make almost none from sun for months at a time.

This is why food and supplements matter. Fatty fish, egg yolks, and fortified milk and cereals contain vitamin D, but few foods contain large amounts. Fortified milk in the US typically provides about 100 IU per cup, which is modest compared to what the skin can make in summer. For people who cannot get reliable sun exposure, supplements are the practical route — and the dose should come from a clinician, not from guesswork.

One clarification worth making: the idea that you can “bank” vitamin D from summer sun for the winter is only partly true. The body stores some vitamin D in fat tissue, and those stores do decline slowly over winter. But for many people, especially in northern latitudes, summer sun alone does not build enough of a reserve to carry them through the darker months.

Does Sun Exposure Have Risks?

Yes. UV radiation from the sun is a known cause of skin cancer, including melanoma, and it also causes skin aging. The World Health Organization and dermatology organizations consistently advise limiting unprotected sun exposure and avoiding burning.

This creates a genuine tension. Sun exposure makes vitamin D, but it also carries real risk. The balance most clinicians strike is this: brief, moderate exposure may be reasonable for some people, but it should never involve burning, and it should not be the only strategy for getting vitamin D. For people at high risk of skin cancer, or those taking medications that increase sun sensitivity, sun exposure for vitamin D is generally not advised.

The honest position is that there is no sun exposure that is risk-free. The goal is to limit risk while meeting vitamin D needs through a combination of sun, food, and — when needed — supplements guided by a clinician.