Not ideal at the same time — calcium can reduce how well your body absorbs iron, so take them at different times of day and check with your pharmacist.
Iron and calcium aren't dangerous together, but calcium can interfere with iron absorption. The NHS states plainly that "calcium can reduce the effect" of iron (ferrous sulfate), and NIH's Office of Dietary Supplements says "calcium might interfere with iron absorption" and that "taking calcium and iron supplements at different times of the day might prevent this problem." The concern is mainly about the iron — that the iron supplement may not work as well — rather than a toxic reaction. Some calcium-containing foods and drinks can have the same effect: the NHS notes that milk (along with tea and eggs) can affect how iron is absorbed, so this isn't only about calcium pills.
Separate the doses by taking iron and calcium at different times of day, as the NIH Office of Dietary Supplements suggests, rather than swallowing them together. A common approach is iron on an empty stomach or away from milk and dairy, with calcium at a different meal; if your pharmacist recommends a specific gap (some clinicians suggest leaving a couple of hours), follow their advice for your situation. If you take iron for diagnosed iron-deficiency anaemia, getting this spacing right matters so the iron actually works — watch for ongoing tiredness, breathlessness, or pallor that suggests the iron isn't being absorbed, and mention it to your clinician. Tell your pharmacist or doctor about all supplements you take, especially ones containing iron, calcium, magnesium, or zinc, so they can advise on timing. Iron supplements can also cause constipation, stomach upset, and dark stools, and high-dose iron is dangerous in overdose — keep iron-containing products out of the reach of children, as accidental iron poisoning is a leading cause of fatal poisoning in young children. This is general information, not a substitute for personalized advice — confirm your own dosing and timing with a pharmacist.
This is general reference, not medical advice, and not a guarantee of safety. Interactions depend on your doses, health conditions, and other medicines. Always confirm with your pharmacist or doctor before combining products, and follow the dosing on each label.