Vitamin D Sun Exposure Dose Planner

Quickly estimate how many minutes of midday sun you need to reach a vitamin D target while accounting for UV intensity, the amount of skin exposed, your phototype, and sky conditions.

Total IU of vitamin D you want to synthesise from sun exposure.
Midday UV index for your location.
Estimate the percentage of skin uncovered (arms + legs ≈ 25%).
Fitzpatrick factor: Type I ≈ 1.2, II ≈ 1.1, III = 1.0, IV ≈ 0.85, V ≈ 0.80, VI ≈ 0.65.
Optional. Leave blank for 1.00. Use 0.7 for light clouds, 0.4 for heavy clouds, 0.85 for urban haze.

Examples

  • Target 1,000 IU, UV index 7, 25% skin exposed, Type III factor 1.00 ⇒ Result: 14.29 minutes
  • Target 1,000 IU, UV index 4, 25% skin exposed, Type V factor 0.80, heavy clouds 0.40 ⇒ Result: 31.25 minutes

FAQ

Does window glass count as exposure?

No. Most window glass blocks UVB, which is necessary for cutaneous vitamin D production, so the calculator assumes direct outdoor exposure.

Can I use this for winter at high latitudes?

When the UV index drops below 3, cutaneous vitamin D production is minimal. The calculator will show very long times—use supplements or artificial UVB under medical supervision.

How do sunscreens affect the estimate?

High SPF sunscreens sharply reduce UVB. If you apply sunscreen immediately, increase the cloud factor to a very low value (e.g., 0.2) to reflect reduced synthesis.

Additional Information

  • Outputs the estimated minutes of exposure required to reach the target IU.
  • Baseline synthesis rate assumes 40 IU per UV index per 1% of body exposure for a Type III skin in clear conditions.
  • Adjust the phototype factor to reflect melanin protection—darker skin requires longer exposure to synthesise the same IU.
  • Use supplements or medical guidance if sun exposure is contraindicated or UV index is low for extended periods.

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