Vitamin D is made in the skin from sunlight and helps the body absorb calcium. Deficiency is common in winter, in people with darker skin, older adults and those who cover up or stay indoors. The Endocrine Society defines deficiency as a 25(OH)D below 20 ng/mL (50 nmol/L) and insufficiency as 21–29 ng/mL.
How to use the Vitamin D Calculator
- Age
- BMI 30 or above
- Blood 25(OH)D level (optional)
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter your age and whether you have risk factors. Optionally enter your blood test result to see how it is classified. Treatment of deficiency should be guided by your doctor.
Vitamin D blood levels
| 25(OH)D | nmol/L | Status |
|---|---|---|
| below 12 ng/mL | below 30 | Severe deficiency |
| 12–19 ng/mL | 30–49 | Deficiency |
| 20–29 ng/mL | 50–74 | Insufficiency |
| 30–100 ng/mL | 75–250 | Sufficient |
| above 100 ng/mL | above 250 | Potentially too high |
Inputs explained
| Field | What to enter |
|---|---|
| Age | In years |
| BMI 30 or above | Choose one: No, Yes |
| Blood 25(OH)D level (optional) | Units: ng/mL, nmol/L |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Units: 1 mcg vitamin D = 40 IU; 25(OH)D: 1 ng/mL = 2.496 nmol/L
RDA: 400 IU (under 1), 600 IU (1–70), 800 IU (71+)
Endocrine Society (at risk): 400–1,000 IU (under 1), 600–1,000 IU (1–18), 1,500–2,000 IU (adults); 2–3 × more with obesity
Worked example
Inputs — Age: 40 years; BMI 30 or above: No; Blood 25(OH)D level (optional): 0 ng/mL.
Results — RDA (National Academies) = 600 IU/day; RDA in micrograms = 15 mcg/day; Suggested for people at risk – upper end (Endocrine Society) = 2,000 IU/day; Upper suggestion with obesity = 2,000 IU/day; Upper limit = 4,000 IU/day; Your blood level = Not entered.
Key terms
- 25(OH)D
- 25-hydroxyvitamin D, the blood test for vitamin D status.
- IU
- International unit; 40 IU = 1 mcg.
Frequently asked questions
How much vitamin D should I take?
600 IU (15 mcg) a day for most adults up to 70, 800 IU over 70; people at risk may need more.
How long in the sun do I need?
Roughly 10–30 minutes of midday sun on arms and legs a few times a week in summer, depending on skin type and latitude.
Can vitamin D be toxic?
Yes – very high doses over time can raise blood calcium; stay below 4,000 IU a day unless prescribed.