CALCULATOR
Magnesium Calculator
Your daily magnesium target, an estimate of what your diet supplies, and the elemental supplement dose that closes the gap.
Magnesium plan
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Estimating your magnesium gap
Adult magnesium recommendations sit at roughly 400 to 420 mg daily for men and 310 to 320 mg for women, rising slightly after age 30. National survey data consistently shows average intakes below these figures, particularly in diets low in nuts, seeds, legumes and leafy greens.
This calculator estimates your dietary intake from your eating pattern and shows the gap. The estimate is deliberately rough, because magnesium is spread across many foods rather than concentrated in a few, so a precise figure would require full dietary tracking.
The important detail on the supplement side is elemental content. Supplements list a compound such as magnesium glycinate, and the magnesium inside it is a fraction of that weight. A 500 mg magnesium glycinate capsule may deliver only 50 to 100 mg of actual magnesium, which is why comparing products on the compound weight is misleading.
Targets and the elemental trap
Women 19-30: 310 mg Women 31+: 320 mg
Supplemental upper limit: about 350 mg elemental, separate from food
The upper limit applies to supplements only because magnesium from food is regulated by absorption and excretion without difficulty. Exceeding it from supplements typically causes diarrhoea rather than serious harm in people with normal kidney function, but kidney disease changes that entirely.
Elemental magnesium by form
| Form | Elemental share | Absorption | Digestive effect |
|---|---|---|---|
| Oxide | About 60% | Poor | Laxative |
| Citrate | About 16% | Good | Mildly laxative |
| Glycinate | About 14% | Good | Gentle |
| Malate | About 15% | Good | Gentle |
| Threonate | About 8% | Good | Gentle, expensive |
Note the tension in that table. Oxide has the highest elemental share by weight but the worst absorption, which is why a high number on the label does not translate into magnesium in your bloodstream. Glycinate has a low elemental share, meaning more capsules, but delivers more of what you swallow.
Magnesium in food
| Food | Serving | Magnesium |
|---|---|---|
| Pumpkin seeds | 30 g | 156 mg |
| Chia seeds | 30 g | 111 mg |
| Almonds | 30 g | 80 mg |
| Spinach, cooked | 100 g | 87 mg |
| Cashews | 30 g | 74 mg |
| Black beans, cooked | 100 g | 70 mg |
| Dark chocolate 70% | 30 g | 65 mg |
| Avocado | 1 medium | 58 mg |
| Oats, dry | 50 g | 60 mg |
| Wholemeal bread | 2 slices | 46 mg |
Who is most likely to be short
- Diets built on refined grains and low in nuts, seeds, legumes and greens.
- Older adults, who absorb less and excrete more.
- People with type 2 diabetes, through increased urinary losses.
- People with gastrointestinal conditions affecting absorption, including coeliac and Crohn disease.
- Long-term users of proton pump inhibitors, where low magnesium is a documented association.
- Heavy alcohol use, which increases excretion.
Blood magnesium is a poor marker of status, because the body maintains serum levels tightly by drawing on bone stores. A normal blood test does not rule out low total-body magnesium, which is one reason intake estimation from diet is a practical starting point.
Frequently asked questions
How much magnesium do I need daily?
What is the supplemental upper limit?
Which form absorbs best?
Can I get enough from food?
Sources
- National Institutes of Health, Office of Dietary Supplements. Magnesium fact sheet for health professionals. ods.od.nih.gov
- Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride, 1997.
- Schwalfenberg GK, Genuis SJ. The Importance of Magnesium in Clinical Healthcare. Scientifica, 2017.
- National Institutes of Health, Office of Dietary Supplements. Nutrient fact sheets. ods.od.nih.gov
- NHS. Nutrition and health guidance. nhs.uk
- US Departments of Agriculture and Health and Human Services. Dietary Guidelines for Americans, 2025-2030. dietaryguidelines.gov
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General information, not medical advice. Consult a qualified professional before changing your diet, especially with a medical condition.