Vitamin D Intake Calculator: Daily Recommended Amount (IU and mcg)
Vitamin D is a fat-soluble nutrient that plays a critical role in calcium absorption, bone mineralisation, immune function, and cell growth. Unlike most vitamins, the body can synthesise vitamin D through sun exposure, but dietary intake and supplementation are important for many people who live at higher latitudes, spend most of their time indoors, or have darker skin pigmentation. The Recommended Dietary Allowance (RDA) for vitamin D is set by the National Institutes of Health (NIH) and varies by age and life stage. For most people aged 1 to 70, the RDA is 600 IU (15 mcg) per day. For adults over 70, the requirement increases to 800 IU (20 mcg) per day, because ageing reduces the skin's ability to synthesise vitamin D and kidney conversion of vitamin D to its active form becomes less efficient. Pregnant and breastfeeding people at any adult age need 600 IU per day. Vitamin D is measured in two units: International Units (IU) and micrograms (mcg). The conversion is 1 mcg equals 40 IU. This calculator shows your recommended intake in both units, plus the tolerable upper intake level you should not exceed without medical supervision. Always consult a healthcare provider before starting high-dose vitamin D supplementation.
Your recommended daily vitamin D intake is -- IU (-- mcg per day).
How vitamin D recommendations are calculated
The NIH Recommended Dietary Allowance for vitamin D is expressed in both International Units (IU) and micrograms (mcg). The conversion between units is fixed:
IU to mcg: mcg = IU / 40
mcg to IU: IU = mcg * 40
Example: 600 IU = 600 / 40 = 15 mcg
Worked example
A 45-year-old woman (not pregnant or breastfeeding):
- Age group: 19 to 70 years
- RDA: 600 IU per day
- In mcg: 600 / 40 = 15 mcg per day
- Tolerable upper limit: 4,000 IU (100 mcg) per day
NIH Vitamin D RDA table by age and life stage
| Life stage / Age | RDA (IU/day) | RDA (mcg/day) | Upper limit (IU/day) |
|---|---|---|---|
| Infants 0 to 6 months | 400 (AI) | 10 (AI) | 1,000 |
| Infants 7 to 12 months | 400 (AI) | 10 (AI) | 1,500 |
| Children 1 to 3 years | 600 | 15 | 2,500 |
| Children 4 to 8 years | 600 | 15 | 3,000 |
| Ages 9 to 70 years | 600 | 15 | 4,000 |
| Ages 71+ years | 800 | 20 | 4,000 |
| Pregnant (14 to 50 years) | 600 | 15 | 4,000 |
| Breastfeeding (14 to 50 years) | 600 | 15 | 4,000 |
AI = Adequate Intake (used when insufficient evidence exists to establish an RDA). All other values are RDAs. Source: NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals, 2024.
Why older adults need more vitamin D
Adults over 70 have a higher RDA (800 IU vs. 600 IU) for two reasons. First, skin becomes less efficient at synthesising vitamin D from sunlight with age. Second, the kidneys become less effective at converting vitamin D into calcitriol, its biologically active form. Older adults are also more likely to have limited sun exposure due to reduced mobility and time spent indoors.
A blood test measuring serum 25-hydroxyvitamin D (25(OH)D) is the standard way to assess vitamin D status. The NIH defines sufficiency as 50 nmol/L (20 ng/mL) or above for most people, though some researchers and clinical groups advocate for higher thresholds. Speak with your doctor about interpreting your results.
Vitamin D calculator: frequently asked questions
How much vitamin D do adults need per day?
The NIH recommends 600 IU (15 mcg) per day for adults aged 1 to 70, and 800 IU (20 mcg) per day for adults over 70. Pregnant and breastfeeding people of any adult age also need 600 IU per day. These are the Recommended Dietary Allowances (RDA), which cover the needs of 97 to 98 percent of healthy individuals.
What is the tolerable upper intake level (UL) for vitamin D?
The NIH sets the tolerable upper intake level for vitamin D at 4,000 IU (100 mcg) per day for adults aged 19 and older. Regularly exceeding this level may lead to vitamin D toxicity, which can cause hypercalcemia (too much calcium in the blood), nausea, weakness, and kidney damage. The UL applies to supplement intake, not sun exposure.
What is the difference between IU and mcg for vitamin D?
IU (International Units) and micrograms (mcg) are two ways to express vitamin D amounts. The conversion is straightforward: 1 mcg of vitamin D equals 40 IU. So 600 IU equals 15 mcg, and 800 IU equals 20 mcg. Both units appear on supplement labels and in nutrition guidelines, so knowing the conversion helps you compare products accurately.
Should I get a blood test to check my vitamin D level?
A blood test for 25-hydroxyvitamin D (25(OH)D) is the most reliable way to assess your vitamin D status. The NIH defines vitamin D deficiency as a serum level below 20 nmol/L (8 ng/mL) and adequacy as 50 nmol/L (20 ng/mL) or above. Your doctor can interpret results in the context of your diet, sun exposure, skin tone, age, and health conditions.
Can I get enough vitamin D from sunlight alone?
Sun exposure triggers vitamin D synthesis in the skin, but the amount produced depends on time of day, season, latitude, skin pigmentation, sunscreen use, age, and cloud cover. In many northern or southern latitudes during winter months, sun exposure may be insufficient. The NIH notes that dietary intake and supplementation become more important when sun exposure is limited. Consult a healthcare provider about your individual needs.
Official sources
- NIH Office of Dietary Supplements: Vitamin D Fact Sheet for Health Professionals.
- NIH Office of Dietary Supplements: Vitamin D Fact Sheet for Consumers.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General information only, not medical advice.