How to use this calculator

Enter your age and rough sun exposure. If you know your current supplement dose or a recent 25(OH)D blood level, add those too for a more specific picture.

What your result means

This shows general population reference ranges from the NIH Office of Dietary Supplements (RDA 600 IU/day for most adults, 800 IU/day for 71+; Tolerable Upper Intake Level 4,000 IU/day) — not a personalized prescription. It deliberately never suggests a dose above that Upper Limit, and if your known blood level is low, it points you to a doctor for a monitored repletion plan rather than a specific self-directed dose, since correcting an actual deficiency safely needs monitoring a doctor can provide.