Vitamin D in Seattle

Seattle’s latitude drives the astronomical portion of this estimate; the fixed cloud assumption must be customized to explore different conditions. Location affects possible vitamin D production from sunlight; it does not change the age-based dietary reference intake or determine whether a particular person needs a supplement.

See Seattle's sunlight estimate in the calculator

What the monthly model shows

The chart uses latitude 47.6062°, longitude -122.3321°, and elevation 53 m. It is model version 2026.09 with reference year 2026. It is not a weather forecast or measured local UV record.

Modeled daily IU from 30 minutes between 10:00 and 14:00 local solar time, skin type II, long sleeves and pants (15% exposed), 40% cloud cover, grass surface, and SPF 0. Customize every input.
Monthly modeled vitamin D production and gap to adult RDA in Seattle
MonthModeled sunlightGap to RDA*
January5 IU/day1,795 IU/day
February49 IU/day1,751 IU/day
March254 IU/day1,546 IU/day
April815 IU/day985 IU/day
May1,557 IU/day243 IU/day
June2,299 IU/day0 IU/day
July2,479 IU/day0 IU/day
August1,892 IU/day0 IU/day
September948 IU/day852 IU/day
October221 IU/day1,579 IU/day
November20 IU/day1,780 IU/day
December2 IU/day1,798 IU/day

*Mathematical gap after modeled sunlight and an assumed 200 IU/day from food. This is not a supplement recommendation.

How much vitamin D do adults need?

US dietary reference amounts are 600 IU (15 µg) daily from all sources for adults through age 70 and 800 IU (20 µg) after age 70. Individual treatment needs cannot be inferred from latitude.

Read the current NIH Office of Dietary Supplements guidance

Vitamin D and seasonal depression

Seasonal affective disorder is a form of depression related to seasonal changes in daylight. Low vitamin D can coexist with it, but research on vitamin D as a SAD treatment is mixed. Established options include clinician-guided light therapy, psychotherapy, and medication. Read the evidence guide to vitamin D and SAD.