Tool
Supplement upper limit checker
Type in the dose from your supplement label and see how close it is to the daily upper limit. It converts IU for vitamins D, A and E.
Calculator
Is your supplement over the upper limit?
Enter the amount on the label.
Upper limits are the Food and Nutrition Board values in the NIH Office of Dietary Supplements fact sheets, checked 5 October 2026. A UL is the most a healthy person can take daily without likely harm, not a target. It does not apply to doses a doctor prescribes and supervises. Not for pregnancy-specific advice; ask your doctor.
The 15 upper limits, adults 19 and older
| Nutrient | Upper limit a day | What counts toward it |
|---|---|---|
| Vitamin D | 4,000 IU (100 mcg) | Food and supplements |
| Zinc | 40 mg | Food and supplements |
| Magnesium | 350 mg | Supplements only |
| Calcium | 2,500 mg (19–50), 2,000 mg (51+) | Food and supplements |
| Iron | 45 mg | Food and supplements |
| Vitamin A (preformed) | 3,000 mcg RAE | Retinol and esters only |
| Vitamin E | 1,000 mg | Supplemental alpha-tocopherol |
| Vitamin C | 2,000 mg | Food and supplements |
| Vitamin B6 | 100 mg | Food and supplements |
| Niacin | 35 mg | Supplements and fortified foods |
| Folic acid | 1,000 mcg | Supplements and fortified foods |
| Selenium | 400 mcg | Food and supplements |
| Iodine | 1,100 mcg | Food and supplements |
| Copper | 10,000 mcg | Food and supplements |
| Choline | 3,500 mg | Food and supplements |
Values are the Food and Nutrition Board's Tolerable Upper Intake Levels as published in the NIH Office of Dietary Supplements health-professional fact sheets, read on 5 October 2026. Limits for 14 to 18 year olds are lower for most nutrients, and the calculator applies them.
Why it matters
Supplement doses are not capped by law. In our label surveys, the most common vitamin D dose on sale was above the limit, as we found in our vitamin D supplement review, and many zinc products allow more than 40 mg a day, as set out in our zinc supplement review.
Frequently asked questions
What is the upper limit for vitamin D?
4,000 IU (100 mcg) a day for everyone aged 9 and over, counting food and supplements together. In our survey of 1,212 vitamin D products, the most common dose was 5,000 IU, above that limit.
What is the upper limit for magnesium?
350 mg a day of magnesium from supplements and medications for adults. Magnesium in food does not count toward it.
What does an upper limit mean?
The Tolerable Upper Intake Level is the maximum daily intake unlikely to cause adverse health effects in healthy people. It is a ceiling, not a target, and it does not apply to doses a doctor prescribes and monitors.
Do European limits differ?
For some nutrients, yes. In 2023 the European Food Safety Authority set adult limits of 12 mg a day for vitamin B6, against the US 100 mg, and 255 mcg a day for selenium, against the US 400 mcg.
Sources
NIH Office of Dietary Supplements, Health Professional Fact Sheets for vitamin D, zinc, magnesium, calcium, iron, vitamin A, vitamin E, vitamin C, vitamin B6, niacin, folate, selenium, iodine, copper and choline: Tolerable Upper Intake Levels tables, unit conversions (1 mcg vitamin D = 40 IU; 1 IU retinol = 0.3 mcg RAE; 1 IU natural vitamin E = 0.67 mg, synthetic = 0.45 mg; 0.6 mcg folic acid = 1 mcg DFE) and scope notes. EFSA 2023 values for B6 and selenium as cited in those fact sheets. Checked 5 October 2026.