Vitamin D Repletion Calculator

About this calculator

Vitamin D status is measured by blood 25-hydroxyvitamin D [25(OH)D] level, and clinical guidelines classify results under 20 ng/mL as deficiency and 20–29 ng/mL as insufficiency, with 30 and above considered sufficient. Correcting a low level usually calls for a short course of high-dose vitamin D rather than a slow daily maintenance dose.

A commonly used regimen gives 50,000 IU of vitamin D once weekly — for 8 weeks in deficiency (under 20 ng/mL), or 6 weeks in insufficiency (20–29 ng/mL) — followed by retesting and a switch to a maintenance dose, typically 1,000–2,000 IU a day.

Primary care physicians use loading regimens like this because vitamin D is fat-soluble and absorbed slowly, so a single large weekly dose raises blood levels more reliably in a short window than an equivalent daily amount split into small doses. This tool is for reference only, not medical advice — actual dosing should be confirmed with a clinician.