Type the vitamin D on your label in IU, mcg or mg. You get it in all three units, and where it sits between the RDA for your age and the upper limit — both from the NIH Office of Dietary Supplements.
2,000 IU is
50 mcg 0.05 mg · between the RDA and the upper limit
This is not medical advice and it does not diagnose anything — whether you are low in vitamin D is a blood test, not a calculator. If you take medication (especially steroids, some diuretics, or anything for your heart or kidneys) or have been prescribed vitamin D, follow your doctor’s or pharmacist’s dose.
How much vitamin D should you take? The NIH’s recommended amount (RDA) is 600 IU (15 mcg) a day from age 1 to 70 and 800 IU (20 mcg) over 70, and the upper limit for everyone from age 9 is 4,000 IU (100 mcg). To convert, 1 mcg = 40 IU. Type your label’s amount and this page converts it and shows where it sits between the two.
How to use it
Type the vitamin D on your label — add up every supplement that has it, a multivitamin included — and tap the unit the label uses: IU, mcg or mg. Pick your age, and pregnant or breastfeeding if that applies. Tapping a different unit converts the number you typed, so the amount stays the same.
The RDA and the upper limit, by age
| Age | RDA | Upper limit |
|---|---|---|
| 0–6 months | 400 IU (10 mcg) — AI | 1,000 IU (25 mcg) |
| 7–12 months | 400 IU (10 mcg) — AI | 1,500 IU (38 mcg) |
| 1–3 years | 600 IU (15 mcg) | 2,500 IU (63 mcg) |
| 4–8 years | 600 IU (15 mcg) | 3,000 IU (75 mcg) |
| 9–13 years | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
| 14–18 years | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
| 19–50 years | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
| 51–70 years | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
| Over 70 | 800 IU (20 mcg) | 4,000 IU (100 mcg) |
Under a year old the figure is an Adequate Intake (AI), not an RDA. Pregnancy and breastfeeding have the same figures as other adults: 600 IU and 4,000 IU. MedlinePlus prints the same numbers. The upper limit is “maximum daily intake unlikely to cause adverse health effects” — from food and supplements together — and the RDA assumes “minimal sun exposure”.
IU, mcg and mg
| IU | mcg | mg |
|---|---|---|
| 400 IU | 10 mcg | 0.01 mg |
| 600 IU | 15 mcg | 0.015 mg |
| 800 IU | 20 mcg | 0.02 mg |
| 1,000 IU | 25 mcg | 0.025 mg |
| 2,000 IU | 50 mcg | 0.05 mg |
| 4,000 IU | 100 mcg | 0.1 mg |
| 5,000 IU | 125 mcg | 0.125 mg |
| 10,000 IU | 250 mcg | 0.25 mg |
| 50,000 IU | 1,250 mcg | 1.25 mg |
The 40 is specific to vitamin D. Other vitamins convert differently, so an “IU to mg” number for vitamin A or E is not this one.
Not everyone needs a supplement
The Endocrine Society’s 2024 guideline, as NIH ODS summarises it, “recommends routine vitamin D supplementation for children and teens age 1 to 18 years, pregnant women, adults with pre-diabetes, and adults age 75 years and older, but not for healthy adults age 19 to 74”. It “does not recommend specific doses but notes that all individuals should adhere to the RDA”. The calculator shows that line next to your result, because a page that only showed doses would read like an advert for supplements.
Worked examples
- 2,000 IU a day, age 35. That is 50 mcg or 0.05 mg: between the RDA (600 IU) and the upper limit (4,000 IU), at 50% of the limit. On a label’s Daily Value (20 mcg) it prints as 250%.
- 1,000 IU a day, age 72. 25 mcg: above the over-70 RDA of 800 IU and at 25% of the 4,000 IU limit.
- A 50,000 IU capsule, taken every day. 1,250 mcg or 1.25 mg: 46,000 IU above the adult upper limit. The calculator places it above the limit and sends you to your doctor or pharmacist; it never calls it a dose to take.
- A baby on 400 IU drops. That is the Adequate Intake for 0–6 months; the upper limit at that age is 1,000 IU.
Common mistakes
- Counting one bottle. A multivitamin, a calcium-with-D tablet and a D3 capsule add up — the limit is for the total.
- Mixing up mcg and mg. 50 mcg is 0.05 mg. A label that says “50 mg” of vitamin D would be 2,000,000 IU — check the unit.
- Reading the Daily Value as the limit. 250% of the DV is not 250% of anything dangerous; the DV (20 mcg) is a labelling reference, the UL (100 mcg) is the limit.
- Guessing your level. Whether you are low is a blood test your doctor orders, not something a dose calculator can tell.
Frequently asked questions
How much vitamin D3 should I take daily?
The NIH RDA — from food and supplements together — is 600 IU (15 mcg) from age 1 to 70 and 800 IU (20 mcg) over 70. The Endocrine Society does not recommend routine supplements for healthy adults aged 19 to 74, and where it does recommend them it names no dose beyond the RDA.
How much vitamin D should a woman take per day?
The same as a man: 600 IU (15 mcg) a day up to age 70, 800 IU over 70. Pregnancy and breastfeeding are 600 IU as well, with the same 4,000 IU upper limit.
How much vitamin D3 is too much?
The upper limit for everyone aged 9 and over is 4,000 IU (100 mcg) a day. NIH ODS notes that signs of toxicity are unlikely below 10,000 IU a day, but also that intakes under the limit “might have adverse health effects over time” — the limit is a ceiling, not a target.
What are the symptoms of too much vitamin D?
Too much vitamin D raises blood calcium, and NIH ODS lists what that can cause: “nausea, vomiting, muscle weakness, neuropsychiatric disturbances, pain, loss of appetite, dehydration, polyuria, excessive thirst, and kidney stones”. It is “almost always a result of excessive intakes of vitamin D through supplements”. Only a blood test confirms it.
How do I convert IU to mcg?
Divide by 40: 1,000 IU is 25 mcg, 2,000 IU is 50 mcg, 4,000 IU is 100 mcg. From mcg to IU, multiply by 40.
How do I convert mg to IU for vitamin D?
Multiply by 40,000: 1 mg is 1,000 mcg, and each mcg is 40 IU. So 0.025 mg is 1,000 IU. The factor is for vitamin D only.
Read next
- Does vitamin D increase dopamine? A look at the science
- Multivitamins for adults — how to choose one, and how much D it already holds.
- Vitamin compatibility — what to take together.
- The best vitamins for women at 30+
This is not medical advice, and nothing here diagnoses or treats anything. If you have been prescribed vitamin D, follow that dose, and talk to your doctor or pharmacist before adding more — especially if you take medication or have kidney, heart or calcium problems. Some links on this site are affiliate links: I buy what I review at full price, and a commission never changes a verdict.