When to take Calcium
Also known as Calcium carbonate, Calcium citrate
Take calcium with food, and if your daily supplement is more than 500 mg, split it into smaller doses because the body absorbs 500 mg or less at a time best. Keep it at least 2 hours away from iron supplements.
Last reviewed October 13, 2026
Timing
| Best time | Split: morning and evening |
|---|---|
| Food | With a meal |
| Fat-soluble | No |
- Absorption is highest at doses of 500 mg or less, so split larger amounts across the day.
- Calcium carbonate is best taken with a meal. Calcium citrate can be taken with or without food.
- In general, any calcium supplement is absorbed better when taken with food.
- Taking smaller doses more often, or with meals, can ease gas, bloating and constipation.
- Vitamin D helps your gut absorb calcium.
Keep apart
Check with your doctor first if…
- Upper limit: 2,500 mg a day for adults 19–50 and 2,000 mg a day for adults 51 and older, from food and supplements together.
- Kidney stones: higher supplement intakes might raise the risk of kidney stones, though later reviews did not confirm this.
- Thyroid medicine: do not take levothyroxine within 4 hours of calcium carbonate.
- Antibiotics (quinolones such as ciprofloxacin): take the antibiotic 2 hours before or 2 hours after calcium.
- HIV medicine dolutegravir: take it 2 hours before or 6 hours after calcium. If you take lithium, ask your doctor first.
- Side effects: gas, bloating and constipation, more often with calcium carbonate.
Amounts studied
RDA: 1,000 mg a day for adults 19–50 and men 51–70; 1,200 mg a day for women 51+ and everyone over 70. UL: 2,500 mg a day (ages 19–50) and 2,000 mg a day (51+). Bone studies often used 500–1,200 mg a day with vitamin D. Calcium carbonate is 40% calcium and calcium citrate is 21%; the label lists elemental calcium.
Follow the serving size on your product’s label.
What the research says
| Area | Evidence | Summary |
|---|---|---|
| Bone health | Moderate | Reviews of trials show calcium, especially with vitamin D, increases bone density in older adults. Results on fractures are mixed, and experts say more research is needed.[1] |
Questions
Should I take calcium in the morning or at night?
We found no source showing a best time of day. What matters is taking it with food and keeping each dose at 500 mg or less.
Can I take calcium and iron together?
It is better not to. Calcium may reduce iron absorption, so experts suggest taking them at different times. MedlinePlus says to wait at least 2 hours after calcium before taking iron.
Calcium carbonate or calcium citrate: which is better?
Carbonate has more calcium per pill (40% vs 21%) but is best taken with a meal. Citrate can be taken without food and causes fewer stomach side effects, especially in older adults with less stomach acid.
Can I take calcium with vitamin D?
Yes. Vitamin D helps your gut absorb calcium, and many bone studies used both together.
Can I take calcium with my thyroid medicine?
Not close together. The levothyroxine label says not to take it within 4 hours of calcium carbonate.
Plan your whole routine
Add Calcium and everything else you take to the planner to see your morning, midday and evening, and what to keep apart.
Open the plannerSources
- Calcium: Fact Sheet for Health Professionals, NIH ODS (accessed October 13, 2026)
- Taking iron supplements, MedlinePlus (accessed October 13, 2026)
- Calcium and bones, MedlinePlus (accessed October 13, 2026)
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. It is general information, not medical advice: talk with your doctor or pharmacist before starting a supplement, especially if you are pregnant, breastfeeding, take medicine or have a health condition.