Calculator

Vitamin D Repletion Calculator

Estimate the D3 dose needed to reach your target 25-hydroxyvitamin D level.

Current 25-OH level (ng/mL)

From your most recent blood test

Target level (ng/mL)

40-60 ng/mL is a common functional target

Body weight

Timeframe (weeks)

8-12 weeks is typical for repletion

BMI category

Vitamin D is fat-soluble. Higher body fat requires higher doses for the same serum response.

Normal weight Overweight Obese

How this works

This calculator uses the dose-response relationship established by multiple clinical trials showing that each 1,000 IU of daily vitamin D3 raises serum 25-OH by approximately 7-10 ng/mL in normal-weight adults over 8-12 weeks. The actual response varies with baseline level (lower baseline = steeper initial rise), body composition (adipose tissue sequesters D3), and individual absorption differences.

The model applies a correction factor for BMI: overweight individuals typically need 1.5x and obese individuals 2-3x the dose of normal-weight individuals to achieve the same serum response. This is consistent with Endocrine Society guidelines recommending 2-3x higher doses for obese patients.

Important: Doses above 4,000 IU/day should be monitored with follow-up labs. Doses above 10,000 IU/day carry risk of hypercalcemia and should only be used under direct clinical supervision. This calculator provides estimates; individual response varies. Always confirm with your provider.

D3 vs D2: Cholecalciferol (D3) is preferred over ergocalciferol (D2) for repletion. D3 is approximately 87% more effective at raising and maintaining serum 25-OH levels. This calculator assumes D3.

References

Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911-1930.

Heaney RP, et al. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr. 2003;77(1):204-210.

Ekwaru JP, et al. The importance of body weight for the dose response relationship of oral vitamin D supplementation and serum 25-hydroxyvitamin D in healthy volunteers. PLoS One. 2014;9(11):e111265.