How this calculator works
The DRI tables provide ordinary daily intake targets and upper levels. Vitamin D activity converts at 40 IU per microgram. An optional blood result uses the common clinical approximation 1 ng/mL = 2.5 nmol/L and the NASEM interpretation summarised by NIH ODS. These categories are not treatment thresholds or a formula for replacing a deficiency. Height, body weight and obesity do not determine a treatment dose in this tool. The result is an estimate for information only and is not medical advice.
Formula
Vitamin D IU = 40 x micrograms. Serum nmol/L is approximately 2.5 x ng/mL. Ordinary RDA is 15 mcg (600 IU) from age 1 through 70, and 20 mcg (800 IU) after 70; infants use a 10 mcg AI.
Worked example
600 IU equals 15 mcg. A blood result of 20 ng/mL converts to approximately 50 nmol/L. A person aged 75 has an ordinary intake reference of 20 mcg/day.
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Frequently asked questions
Does low blood vitamin D tell me what dose to take?
No. Treatment depends on the clinical setting, cause, medicines and monitoring.
Is the upper level a useful target?
No. It is a safety reference for usual intake, not a goal.
Why is obesity not a dose multiplier?
A universal weight-based replacement rule is not established by the ordinary DRI tables. Individual treatment needs professional assessment.