Vitamin D Dosage Calculator (Free): Your Daily IU Target
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The quick answer: the recommended intake is 600 IU (15 mcg) a day for adults up to 70 and 800 IU (20 mcg) after 70 (NIH Office of Dietary Supplements), and the 2024 Endocrine Society guideline found no added benefit above that for most healthy adults under 75. Many people take 1,000–2,000 IU, which stays well under the 4,000 IU (100 mcg) daily upper limit. Choose D3 (not D2) and take it with a meal that contains fat. The calculator below turns your goal, sun exposure and preferred form into a personal range.
Free Tool
Vitamin D dosage calculator: your daily IU target
Answer three questions and get an evidence-based vitamin D3 dose, whether to add K2, and how to take it.
General maintenance
Bone & immune support
Low mood in winter
Correcting a known deficiency
Regular midday sun
Some sun
Little (indoors, winter, northern, darker skin)
D3 softgel
D3 + K2
Vegan D3 (lichen) drops
Your daily D3 dose
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Adjust for sun & season
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Best form for you
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Why this dose
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The form your answers point to
Vitamin D3 softgelTake it with a meal that contains fat. Softgels already carry oil.
Based on NIH ODS intake levels (RDA 600–800 IU, upper limit 4,000 IU) and the 2024 Endocrine Society guideline. Routine blood testing is not recommended for healthy adults; deficiency treatment should be supervised by a doctor.
A convenient D3+K2 combination in one softgel. Note: 5,000 IU is above the 4,000 IU adult upper limit, so take it only if your doctor confirms a deficiency; most adults need 600–800 IU a day (NIH).
5,000 IU D3 + 100mcg K2 MK-7 per softgel (above the 4,000 IU upper limit)
Coconut oil base — maximizes fat-soluble absorption
RDA is 600 IU (800 IU over 70); the 2024 Endocrine Society guideline found no extra benefit above it for most healthy adults under 75
Bone & immune
2,000 IU (50 mcg)
Yes (MK-7)
K2 steers calcium into bone rather than arteries
Low winter mood
2,000–4,000 IU (50–100 mcg)
Yes at 4,000+
Higher end only in the darkest months; step back down in spring
Correcting deficiency
4,000 IU (100 mcg) — supervised
Yes
For 25-OH below 20 ng/mL; retest after 8–12 weeks
1 mcg of vitamin D = 40 IU. The Tolerable Upper Intake Level for adults is 4,000 IU/day without medical supervision. Routine blood testing is not recommended for healthy adults (Endocrine Society, 2024); if your doctor tests you, 20 ng/mL (50 nmol/L) or more is sufficient for most people, and levels above 50 ng/mL (125 nmol/L) can be associated with adverse effects (NIH ODS).
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How to take vitamin D so it works
⭐ Our Verdict
Our Verdict on Vitamin D3
Vitamin D3 is worth taking if you are low or likely to be: little sun, older age or darker skin. Most adults need 600-800 IU a day and the adult upper limit is 4,000 IU (NIH). More is not better: in the large VITAL trial, 2,000 IU a day did not prevent depression in adults over 50.
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Dosage Quick Reference
D3 dosing at a glance (NIH)
Diagnosed deficiency
Doctor-set dose
Higher doses only under supervision
Recommended intake
600-800 IU
600 IU to age 70, 800 IU after
Blood level
20+ ng/mL
Sufficient for most people
Form
D3 (cholecalciferol)
Not D2 — 87% more potent
Take With
Fatty meal
Peak levels 32% higher in one trial
Upper limit
4000 IU/day
Adults, all sources
⚠️ Routine testing is not recommended for healthy adults (Endocrine Society, 2024). Stay at or under 4,000 IU a day unless a doctor advises otherwise; toxicity is rare but possible with prolonged high-dose use.
Always pick D3, not D2. D3 (cholecalciferol) is about 87% more effective than D2 at raising and holding your blood level.
Take it with a fatty meal. Vitamin D is fat-soluble; food with some fat markedly improves absorption.
Add K2 (MK-7) at higher doses. Once you take 4,000+ IU, K2 helps direct the extra calcium into bone rather than soft tissue.
Vegan? Lichen-derived D3 is true D3 and far better than plant D2. Oil-based drops absorb well.
Testing is not routine. The 2024 Endocrine Society guideline advises against routine testing in healthy adults; your doctor may test you if you have a condition that affects absorption or bone health.
Based on the NIH Office of Dietary Supplements vitamin D fact sheet and the 2024 Endocrine Society guideline (Demay et al., J Clin Endocrinol Metab 2024). General education, not medical advice — deficiency correction should be supervised by a doctor.
For most healthy adults, the recommended intake is 600 IU (15 mcg) a day, or 800 IU (20 mcg) after age 70 (NIH Office of Dietary Supplements). The 2024 Endocrine Society guideline found no added benefit above that for most people aged 19–74, and suggests extra vitamin D only for children and teens, adults over 75, pregnancy and high-risk prediabetes. Up to 4,000 IU (100 mcg) a day stays within the adult upper limit. If a blood test shows a deficiency, your doctor will set a higher, supervised dose for a limited time.
Severe deficiency can cause bone pain and muscle weakness (osteomalacia), but most people with low vitamin D have no symptoms. The only definitive test is a 25-hydroxyvitamin D blood test (25-OH D). Levels of 20 ng/mL (50 nmol/L) or more are sufficient for most people, and levels above 50 ng/mL (125 nmol/L) can be associated with adverse effects (NIH ODS). Routine testing is not recommended for healthy adults (Endocrine Society, 2024).
Always D3 (cholecalciferol) — it's 87% more potent at raising and maintaining 25-OH levels compared to D2 (ergocalciferol). D3 is the form your skin makes from sunlight and the form found in fatty fish. D2 is derived from plants/fungi and is less bioavailable. Most prescriptions use D2 for historical reasons; over-the-counter D3 is superior.
Not strictly necessary for vitamin D's immune, muscle, and mood benefits. However, K2 (MK-7 form) works synergistically with D3: it activates osteocalcin (which directs calcium into bones) and matrix GLA protein (which prevents calcium from depositing in arteries). At higher D3 doses (4,000+ IU), some experts suggest adding K2 (90–200 mcg MK-7), although the evidence is still limited.
Only a few foods are rich in it. NIH figures: cooked sockeye salmon about 570 IU per 3 oz, farmed rainbow trout about 645 IU, one egg about 44 IU, canned light tuna about 40 IU per 3 oz, and fortified milk about 120 IU per cup. Fatty fish and fortified foods make the 600–800 IU target reachable. Sunlight also makes vitamin D in your skin, but how much depends on season, latitude, time of day and skin type.
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