# Vitamin D Calculator

URL: https://speedycalculator.com/calculators/health/vitamin-d/
Last updated: 2026-10-30

> The vitamin D calculator shows the recommended daily vitamin D intake for your age, the amount suggested for people at risk of deficiency, and – if you know your blood level – how your 25(OH)D result is classified, with conversions between IU and micrograms and between ng/mL and nmol/L.

## Inputs

- Age (years)
- BMI 30 or above
- Blood 25(OH)D level (optional) (ng/mL, nmol/L)

## Results

- RDA (National Academies)
- RDA in micrograms
- Suggested for people at risk – upper end (Endocrine Society)
- Upper suggestion with obesity
- Upper limit
- Your blood level

## 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
```

## Explanation

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)Dnmol/LStatusbelow 12 ng/mLbelow 30Severe deficiency12–19 ng/mL30–49Deficiency20–29 ng/mL50–74Insufficiency30–100 ng/mL75–250Sufficientabove 100 ng/mLabove 250Potentially too high

### Inputs explained

FieldWhat to enterAgeIn yearsBMI 30 or aboveChoose one: No, YesBlood 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.*

## 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.

## FAQ

**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.


## Sources

- [Holick MF et al. Evaluation, treatment, and prevention of vitamin D deficiency: Endocrine Society guideline. J Clin Endocrinol Metab, 2011](https://pubmed.ncbi.nlm.nih.gov/21646368/)
- [NIH Office of Dietary Supplements – Vitamin D](https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/)