Calcium builds bones and teeth. Most people should count food first: a supplement only needs to fill the gap.
Calculator Official intake Study doses Best form Works with Safety Sources
PRI (population reference intake)
| Men 18-24 | 1,000 mg |
|---|---|
| Men 25+ | 950 mg |
| Women 18-24 | 1,000 mg |
| Women 25+ | 950 mg |
| Pregnancy 18-24 | 1,000 mg |
| Pregnancy 25+ | 950 mg |
| Breastfeeding 18-24 | 1,000 mg |
| Breastfeeding 25+ | 950 mg |
Safe upper limit: 2,500 mg a day
RDA (recommended dietary allowance)
| Men 18-70 | 1,000 mg |
|---|---|
| Men 71+ | 1,200 mg |
| Women 18-50 | 1,000 mg |
| Women 51+ | 1,200 mg |
| Pregnancy | 1,000 mg |
| Breastfeeding | 1,000 mg |
Safe upper limit: 18-50: 2,500 mg, 51+: 2,000 mg
Source: National Academies (NASEM) 2019
These are doses tested in research, not personal advice. Some exceed the upper limit because they were short courses or given under medical care.
No single dose
Systematic review (BMJ 2015): calcium from food was not linked to fewer fractures, and supplements gave small, inconsistent benefits that disappeared in the best-quality trials. The authors advised against raising calcium intake just to prevent fractures.
Practical pick
Carbonate, salt weight (40% Ca)
Why: Calcium carbonate is 40% calcium, so you need fewer or smaller tablets. It needs stomach acid, so it only works taken with food. In a trial in people who make no stomach acid, fasting absorption was 4% from carbonate against 45% from citrate; taken with breakfast, carbonate absorbed normally.
Alternatives: Calcium citrate is 21% calcium but needs no stomach acid, so pick it if you take a proton pump inhibitor or another acid blocker, or if you cannot take it with a meal. It also causes less gas, bloating and constipation. Absorption is best at 500 mg or less at a time.
Vitamin D is needed to absorb calcium in the gut. Calcium supplements work best when your vitamin D intake is adequate.
Calcium can reduce how much iron you absorb, both from food and supplements. Take them at different times of day.
Elemental shares for salts are typical values. Most EU and US labels already list the elemental amount, so pick the first option when unsure.
Dairy, fortified plant milks, tofu set with calcium, sardines with bones, kale.
Lowers absorption of iron, zinc, thyroid hormone and some antibiotics: take them apart. Carbonate is best taken with food.
The safe limit counts food too. Large single doses absorb poorly; split above about 500 mg.
Pregnant, breastfeeding, on medication, or managing a health condition? Check with a doctor or pharmacist before starting a supplement.
Values checked: November 12, 2026.
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