A vitamin D estimate calibrated for how you actually dress.

Which age range are you in?

Your skin's ability to make vitamin D naturally reduces with age. We use age bands, not your exact age.

• Under 50
• 50 to 65
• Over 65

Bands keep things private. If you are pregnant or breastfeeding, you can flag that at the optional checkout stage later.

How would you describe your natural skin tone?

This is the Fitzpatrick scale, a familiar dermatology shorthand. It describes how your unexposed skin behaves in the sun. Pick the closest match, not a perfect one.

• Type I, very fair Always burns, never tans, often freckled. Ancestrally northern European.
• Type II, fair Usually burns, tans minimally. Ancestrally northern or central European.
• Type III, light olive or wheatish Sometimes burns, gradually tans. Ancestrally southern European, Levantine, North African Mediterranean.
• Type IV, olive or light brown Burns rarely, tans well. Ancestrally Middle Eastern, North African, Mediterranean, lighter South Asian.
• Type V, brown Very rarely burns, deeply tans. Ancestrally South Asian, East African, parts of the Middle East.
• Type VI, deep brown to black Never burns, always pigmented. Ancestrally sub-Saharan African, Afro-Caribbean, parts of South Asia.

Your skin tone reflects the latitude your ancestors lived at. UK latitudes give less UVB than the tones above evolved for. The maths is just maths, not a verdict.

Which best describes your ethnic background?

We use this for the framing of your result, not the maths. The skin tone you picked is what drives the calculation. Pick the closest match, or "Prefer not to say".

• South Asian Pakistani, Bangladeshi, Indian, Sri Lankan, Afghan and related backgrounds
• Middle Eastern or North African Arab, Iranian, Turkish, Kurdish, Berber and related backgrounds
• African Sub-Saharan African, East African, West African backgrounds
• African-Caribbean or Black British
• Southeast Asian or East Asian Malay, Indonesian, Chinese, Filipino and related backgrounds
• White British or White European convert
• Mixed or multiple backgrounds
• Prefer not to say

What does your usual dress outside the home look like?

This is about surface area of skin exposed, not religious correctness. Your modesty practice is your choice; the calculator works around it, not against it.

• Hijab only, otherwise modest dress Long sleeves, ankle-length, face and hands uncovered
• Hijab with abaya or full-body covering Full-body covering, face and hands exposed
• Niqab with hands exposed Face fully covered, hands and forearms uncovered
• Niqab with gloves Eye area is the only skin uncovered
• Modest dress without head covering Long sleeves and trousers preferred, head and hair uncovered
• It varies by context Cover more in some settings, less in others. We factor this in.
• Other, or you prefer to describe

On a sunny summer day, how long are you usually outside in the sun?

Think about a normal day, not your best one. Be honest: most people in the UK get far less real sun than they expect, and from October to March there is almost none to get. Your dress answer already tells us how much skin the sun can reach; this is just about time.

• Almost none, I am mostly indoors Supplementation will be your year-round mechanism
• Up to 15 minutes
• 15 to 30 minutes
• 30 minutes to an hour
• 1 to 2 hours
• More than 2 hours

This is about time with the sun actually out, in summer. UK winter makes almost none either way; this just helps us be honest about your three pathways.

Are you currently taking a vitamin D supplement?

Whatever you are taking now goes into the maths so the gap number reflects your real situation, not a fresh start.

• No, nothing currently
• A general multivitamin Most contain around 200 to 400 IU of vitamin D
• 400 IU (10 µg) daily vitamin D The standard UK over-the-counter and Healthy Start dose
• 1,000 IU (25 µg) daily vitamin D A common higher-strength over-the-counter option
• 2,000 IU (50 µg) daily vitamin D
• Other amount, or I am not sure

For any dose conversation above 4,000 IU per day, the recognised upper level for unsupervised use, your pharmacist or GP is the right next stop. This tool helps you go in informed.