Vitamin D dosage calculator

For most adults, 600 to 800 IU (15 to 20 µg) of vitamin D3 a day meets the RDA, and up to 4,000 IU a day is the safe upper limit without medical supervision. The 2024 Endocrine Society guideline recommends empiric daily supplementation above the RDA for adults over 75, pregnant people, children and prediabetes, and advises against routine blood testing in healthy adults. People with little sun, darker skin, obesity or a low measured level need more; enter your details for an estimate.

Last reviewed: 2026-10-06

How this is calculated

Vitamin D guidance has two layers. The Institute of Medicine (2011) set the RDA (600 IU for ages 1 to 70, 800 IU over 70, 400 IU under 1) and the tolerable upper intake level (4,000 IU for adults). The Endocrine Society 2024 guideline then addressed who should take more than the RDA without testing: children and adolescents, adults over 75, pregnant people, and adults with prediabetes. It recommended against routine 25(OH)D testing in otherwise healthy adults and against high-dose regimens, favouring daily, lower doses.

Group	IOM RDA	Endocrine Society 2024
Infants under 1	400 IU	Supplement (empiric)
1 to 18	600 IU	Supplement above RDA to prevent rickets and respiratory infections
19 to 70	600 IU	RDA unless prediabetes or pregnant
Over 70 / 75	800 IU	Supplement above RDA (lower mortality in trials); doses used were around 1,000 to 2,000 IU
Upper limit	4,000 IU per day (adults) without supervision

Why the adjustments. Body weight: in trials, the rise in blood level per IU falls with body weight, and obese adults need roughly 2 to 3 times the dose for the same level. Skin tone: melanin reduces synthesis, so with the same sun exposure darker skin produces less. Sun: 10 to 20 minutes of midday sun on arms and face in summer at mid latitudes makes 1,000 IU or more, but zero in winter above about 35 degrees latitude.

Blood levels. Under 12 ng/mL (30 nmol/L) is deficient, 12 to 20 is insufficient for bone health, 20 to 50 is adequate for almost everyone, above 50 brings no extra benefit, and above 100 to 150 risks toxicity (high calcium). Doctors treat deficiency with 50,000 IU weekly for 8 weeks or 6,000 IU daily, then maintenance, which this calculator does not prescribe.

Frequently asked questions

How much vitamin D should I take daily?

600 IU (15 µg) for adults to age 70 and 800 IU (20 µg) after, per the IOM. Many people with little sun take 1,000 to 2,000 IU, which is within the 4,000 IU daily upper limit. Over 75, pregnant, or with prediabetes, the 2024 Endocrine Society guideline suggests supplementing above the RDA.

Is 5,000 IU of vitamin D too much?

It exceeds the 4,000 IU tolerable upper limit for unsupervised daily use. It is commonly prescribed short-term for deficiency, but long-term 5,000 IU without monitoring is not recommended. Toxicity (high blood calcium) generally appears above 10,000 IU a day for months, or blood levels above 150 ng/mL.

Should I get my vitamin D level tested?

The 2024 Endocrine Society guideline recommends against routine testing in healthy adults, because the test does not change what you should do. Testing is useful if you have symptoms of deficiency, osteoporosis, malabsorption, kidney disease, or are on high doses.

D2 or D3?

D3 (cholecalciferol). It raises and maintains blood levels more effectively than D2 (ergocalciferol). Vegan D3 from lichen is available.

Can I take vitamin D once a week instead of daily?

Yes. Weekly dosing of 7 times the daily amount gives the same blood levels. Daily was favoured in the 2024 guideline mainly because large monthly or yearly bolus doses were linked to falls in older adults.

Does vitamin D need vitamin K2 or magnesium?

Magnesium is required to activate vitamin D, and deficiency is common, so adequate magnesium intake helps. K2 pairing is popular but trial evidence that it is needed at normal vitamin D doses is weak.

Sources

Demay MB et al. Vitamin D for the prevention of disease: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2024;109(8):1907-1947 (empiric supplementation for over 75, pregnancy, children, prediabetes; against routine testing)
Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. 2011 (RDA 600/800 IU; UL 4,000 IU)
NIH Office of Dietary Supplements. Vitamin D fact sheet for health professionals (blood level thresholds, toxicity)
Ekwaru JP et al. The importance of body weight for the dose response relationship of oral vitamin D supplementation and serum 25-hydroxyvitamin D in healthy volunteers. PLoS One. 2014;9(11):e111265 (dose needed rises with body weight)
Tripkovic L et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr. 2012;95(6):1357-64

Educational information only, not medical advice. Results are population estimates from published studies and may not apply to you.