Iron deficiency is not a fate.
Calculate your deficit.

The Ganzoni formula calculates the individual iron deficit from body weight, the current and target hemoglobin value plus an iron-depot component. The calculator above uses the established formula:

Iron deficit (mg) = BW × (target Hb − actual Hb) × 2.4 + depot iron (500 mg)

The formula has been a clinical standard for decades and is described in the Onkopedia guideline of the German Society of Haematology and Oncology (DGHO, 04/2025). It is meaningful mainly in anemia; without anemia it only shows the storage portion.

Ferritin reflects the iron stores. Laboratory limits often start at 15–30 ng/ml; according to the Onkopedia guideline these reference values have “nothing to do with an ideal value”. There is no single optimal value for everyone – guidelines name thresholds depending on the situation:

· Below 15 ng/ml: iron deficiency confirmed (WHO, Onkopedia/DGHO 04/2025)
· Below 30 ng/ml: iron deficiency likely, an increasingly recommended cut-off (Onkopedia 04/2025); the British guideline names 45 ng/ml as the best trade-off (BSG 2021)
· Below 50 ng/ml with fatigue but no anemia: iron can help (Vaucher 2012); when planning a pregnancy, above 50 ng/ml is recommended (Onkopedia)
· Up to 75 ng/ml or transferrin saturation below 20% in restless legs: iron recommended (German DGN/DGSM guideline; AASM 2025), 75–100 ng/ml by infusion only (AASM)

Inflammation raises ferritin and can mask a deficiency – then CRP and transferrin saturation are needed. I set your individual target with you based on symptoms and findings.

This depends considerably on the route of supplementation:

· Oral supplementation: 3-6 months, depending on absorption, tolerability and severity. For moderate deficiency with good tolerability, this is often the first choice.
· Intravenous supplementation: 1-3 sessions over a few weeks — the calculated total amount is administered in 1-3 infusions. Appropriate for severe deficiency, oral intolerance or absorption disorders.

A ferritin check 6-12 weeks after the end of therapy is medically advisable.

Oral is appropriate for: mild to moderate deficiency, good tolerability, intact absorption, availability of time (3-6 months of therapy).

Intravenous is appropriate for: severe deficiency with a drop in Hb, oral intolerance (gastrointestinal complaints, constipation), absorption disorders (e.g. after gastric surgery, with chronic bowel diseases), a need for rapid therapy (e.g. before surgery), or when oral therapies have repeatedly failed to reach the goal.

The indication should be established by a physician — intravenous supplementation requires a correct diagnosis, an explanation of the risks and the option of emergency care in the rare event of a reaction.

A An iron infusion is appropriate when:

· oral therapies had to be discontinued due to gastrointestinal complaints
· the deficit is clinically relevant and needs to be corrected quickly
· absorption disorders are present (celiac disease, Crohn's disease, after gastric bypass)
· chronic blood loss exceeds oral intake (e.g. heavy menstruation)
· preoperative conditioning is necessary (correction of anemia before surgery)

In my practice we calculate the total amount according to Ganzoni and plan the sessions individually. Information is provided in writing, and emergency equipment is standard.

Iron deficiency can show a broad range of symptoms — often nonspecific and slowly progressive:

· Fatigue and exhaustion, even with normal sleep
· Hair loss (diffuse, often starting at the front)
· Difficulty concentrating, "brain fog"
· Cold hands and feet, feeling cold at normal temperatures
· Brittle nails, cracks at the corners of the mouth
· Restless legs syndrome, restless sleep
· Exertional dyspnea, headaches, dizziness

These symptoms are nonspecific — laboratory confirmation (ferritin, Hb, transferrin saturation) is mandatory before any therapy.

The calculator provides guidance values based on the Ganzoni formula — it does not replace medical diagnosis or the establishment of an indication. Before iron supplementation, laboratory confirmation and, if applicable, an investigation of the underlying cause are required.

We recommend a personal consultation at the practice before any therapy.