Vitamin D Calculator

This calculator uses the Endocrine Society's bands: below 20 ng/mL is deficient, 20-29 ng/mL is insufficient, and 30-100 ng/mL is sufficient. If your lab reports in nmol/L, divide by roughly 2.5 to convert to ng/mL and compare against these same bands.

The dosing follows the Endocrine Society's guideline, and it's not the same number for everyone. Below 20 ng/mL, it suggests a supervised loading course (50,000 IU/week for 8 weeks) followed by 1,500-2,000 IU/day maintenance. Between 20-29 ng/mL, it goes straight to 1,500-2,000 IU/day without a loading dose. At 30-100 ng/mL, the general 600-800 IU/day RDA is enough unless you have risk factors for deficiency.

Those are answers to two different questions. 600-800 IU/day is the Institute of Medicine's RDA for the general population -- people who were never deficient. 1,500-2,000 IU/day is the higher maintenance dose the Endocrine Society recommends specifically for someone who has just corrected a diagnosed deficiency, to keep the level from drifting back down. If your result here shows the higher figure, it's because your entered level was in the deficient or insufficient range.

There's an important distinction here: 100 ng/mL is the Endocrine Society's conservative safety ceiling for supplementation, not the point where toxicity begins. Symptomatic toxicity (hypercalcemia) is generally associated with levels above roughly 150 ng/mL, and it's almost always caused by excessive supplementation, not sun exposure or diet. A result just over 100 is a signal to stop supplementing and recheck, not a medical emergency.

Not necessarily. The Endocrine Society's 2024 guideline update moved away from recommending population-wide testing, since large trials mostly failed to show that supplementing everyone reduces falls, fractures or cardiovascular events. It now suggests that generally healthy adults under 75 can simply take the standard 600-800 IU/day RDA without a blood test, reserving testing and higher-dose supplementation for groups where trials show a clear benefit: ages 1-18, adults 75+, pregnancy, and prediabetes.